Linguists study language in one of two basic ways. They look at language through time, how it changes, and the processes that drive and inform that change. This is called a diachronic approach - 'dia-' meaning 'across'. When applied to what a particular word means we usually refer to this kind of study as etymology. The etymology of the word 'etymology' tells us that the two parts mean: true (eteos) word (logia) and the sense of it is that it reveals the true meaning of the word. [Note the parallel with the Japanese word for mantra: shingon = true word] Or linguists study what language does now, what things mean in the context of the present and in a particular place. This approach is called synchronic - 'syn-' meaning 'together'. Ironically the history of a word can be entirely irrelevant to what it means now. Consider the contemporary meaning of the word 'terrific' which originally meant terrifying!
Just as one can study what a word means these way, we can study what an idea means. In this post I plan to do a potted history of an idea which I am representing by the phrase "spiritual life" in English which equates with the Sanskrit word brahmacarya (it is the same in Pāli). We can begin with an etymology. Brahmacarya is a compound combining the elements brahma and carya. 'Brahma' is the uninflected form of the noun, as we expect in a Sanskrit compound. So it can mean either the transcendent principle of the universe, brahman (neuter tense), or the more concrete manifestation of the creator God, Brahmā (masculine tense). It's important to realise that these two are not necessarily synonymous. Carya more literally means "going about, wandering, walking or roaming, visiting, driving", and in its applied sense means "behaviour, conduct; practising, performing, occupation with, engaging in". The word brahmacarya is used in relation to a number of ideas, and how we understand it depends to a large extent on what time and place we are talking about.
In the early days of the Vedic religion the sages often were faced with, or posed each other, puzzles of a metaphysical nature: for instance they wondered on what did the creator stand when he created the world? Answers to these puzzles were known as brahmans. The Ṛgveda contains many puzzles, and many brahmans. The ancient Vedic world view was one in which the world was wondrous and ordered by a mysterious cosmic principle that they called ṛta. Everything in the world was interconnected and participated in this cosmic order, and maintenance of the cosmic order was a joint project between the gods and the priests. So a brahman was like an insight into the cosmic order. The Vedics also believed that such insights, especially insights into the connections (bandhu) between this world and heaven were important for understanding, and therefore maintaining ṛta. The functional aspect of the Vedic religion was the act of sacrifice, with the sacrificial fire (agni) being the medium of exchange between this world and heaven - such commerce being essential for maintaining ṛta.
Perhaps due to the changing social circumstances - for instance the discovery and use of iron that helped to transform the Ganges plain from forest to farmland - priests began to reflect on their function. In particular they began to believe that it was possible to abstract the sacrificial ritual and perform it in imagination. The texts in which these ideas were first composed were commentaries on the Saṃhita portions of the Vedas and were called brāhmaṇa. Confusingly the priests themselves were now also called brāhmaṇas - I use the Anglacized Brahmin to talk about the priests. It was perhaps at this time that the cosmic order ṛta was reconceptualised as dharma - which can mean both 'nature' and 'duty' thus incorporating similar concepts, but moving in a new direction.
Not long before the Buddha this movement to think about things, to create abstractions, and to work in the imagination, took form in the Upaniṣadic or Vedantic traditions (although the latter terms seems to have come along much later). It is in the Upaniṣads that we meet with the two conceptions I mentioned above: brahman the abstract transcendental principle; and Brahmā the creator god. Of course at this time there are also recorded many other religious traditions, indeed if we read history right there was an explosion of new ideas around this time that coincided with similar processes in other parts of the world. The period has been called the Axial Age. The non-Brahmin sectarians were called śramaṇas - from the root śram meaning to work or toil. Incidentally some linguists think this word śramaṇa comes into English, via Asian and Russian intermediaries, as the word shaman (more on this in a future post).
In this early Upaniṣadic period (also known as the "Late Vedic period") a Brahmin man is described as going through several stages in life or āśramas (incidental from the same root śram). Women are not part of this picture. Different texts describe different numbers of stages, and some see them not as a sequence but as different possible lifestyles, however all seem to include brahmacarya. Taken as a sequence in the early stage of life one was unmarried and this, even today in Indian, is synonymous with being celibate. However celibacy was probably initially incidental for unmarried men, and the importance of this phase of life was that it involved learning and study. The ideal was for a son to study with his father. However some students went to live and study with teachers, and some even wandered from place to place and teacher to teacher. The object of study was still considered to be the Vedas and their associated rituals, but may have included the śastric branches of knowledge as well such as grammar, mathematics and astrology. Conformation of this basic set up are found in early Buddhist texts which frequently refer to Brahmins as well versed in the Vedas and other Brahminical studies. After this period of learning the Brahmin youth might stay with his teacher, but more usually was expected to return home and marry, produce more sons and in turn educate them in the Brahminical lore and procedures.
The Buddha was to some extent limited in how he got his ideas across by the language of the day. Sometimes he simply used existing terms unchanged (eg. tapas asceticism) and sometimes he attempted to redefine a word as in the case of dharma and in this case of brahmacarya. In fact the Buddha attempted to totally redefine the concept of what a Brahmin is - linking it to behaviour rather than birthright. Clearly this latter project failed, but we have inherited this word brahmacarya.
In the early Buddhist texts brahmacarya keeps virtually the same reference, but loses the any sense of sequence. Anyone who is undertaking some kind of spiritual or religious training could be referred to as a brahmacarin. It's quite a common usage in the canon. All bhikkhus were undertaking brahmacarya because they undertake religious vows, study sacred texts, and undertake various religious and ascetic practices. However at some point - and I'm not sure when this happened - the word came to have the much narrower meaning of 'chastity' that is the abstention from any kind of sexual activity (and the vinaya is explicit and exhaustive in proscribing forms of sex!). It's ironic that what was originally a mere coincidence because of the rigid social structures which required that there be no sex before marriage, is not the most important feature of the lifestyle.
To some extent the WBO has revalorised the word, broadening it our again to mean one who doesn't indulge the pleasures of the senses. Someone who undertakes a vow of brahmacarya does refrain from sexual activity, but also undertakes to avoid over stimulating themselves in other ways as well. They may also express this by trying to let go of personal preferences. Someone who takes a life vow of brahmacarya is known in our order an an anagarika. This means one (-ka) who does not have (an-) a home (agara). So another feature of their lives is that they try to minimise possessions and this is usually interpreted especially as including not owning real-estate.
image: from a post on celibacy by Shravasti Dhammika on his blog Dhamma Musings.