In this post: Bodhisattva, anagārikā, samyak/mithyā (Pāli sammā/micchā)
The typical explanation of this word tells us that sattva is the Sanskrit word for 'being', an abstract noun from sat 'true, real', ultimately from the verbal root √as 'to be' (cognate with English 'is'). Sanskrit used the notion of 'being' in much the same way we do in English: being 'a state of existence (or realness) and; a being 'a living entity'. Sat (and its derivative satya) was a very important term in Vedic metaphysics, and is still important in contemporary Hindu metaphysics. Adding the -tva suffix gives 'truth' or 'reality'.Anagārikā
It's plausible enough, however the Pāli commentaries take the Pāli equivalent satta as related to either sakta 'intent on' (the past-participle of the verb √sañj 'clinging'); or from śakta meaning 'capable of' (pp from √śak 'strong, capable, able'). The suggestion then is that sattva is a hyper-sanskritisation similar to sūkta > sutta > sūtra as discussed in Philological Odds and Ends I. In this case Sanskrit satka, śakta and sattva all become satta in Pāli and other Prakrits. The option of 'intent on' (satka) would fit the way 'bodhisattva' practitioners are described in very early Mahāyāna Sūtras (e.g. the Ugraparipṛccha - see Jan Nattier. A Few Good Men).
A bodhisattva, then, is 'intent on bodhi' and perhaps should be spelt bodhisakta (though centuries of tradition weigh against such a correction). The word is an adjective used in the sense of someone aspiring to, or about to, attain bodhi and become a Buddha. Both buddha and bodhi deriving from the same root √budh 'to understand, to wake up to' - buddha is the past-participle meaning 'awoken', while bodhi is verbal noun meaning 'knowledge' (c.f. buddhi 'intelligence').
Note the spelling 'satva' (with a single 't') seems to have begun as a scribal error - inadvertently leaving off the extra 't'. There is a word satvan which is literally 'one who possesses sat', and which is used to mean 'living, breathing' and 'powerful, strong, a warrior'. The nominative singular is satvā, and it is purposefully used in some cases to describe the Buddhas and Bodhisattvas - they are described as mahāsatvā 'great heros' in the Sarvatathāgata-tattvasaṃgraha Tantra for instance. Cf the use of mahāsattva which is commonly used in Mahāyāna sūtras.
Someone asked me about this word. The Sanskrit is anāgarikā (fem) meaning 'homeless'. The word is not in PED, but it does occur 3x in the Cullanidesa (a commentarial text included in the Canon): once as anagārikassa (the dative - to/for the homeless), and twice in the compound anagārikamitto (friend of the homeless). This seems to be the only use in Pāli and I deduce that the word is masculine or neuter in Pāli 'anāgarika' (short final 'a'). Given that is doesn't occur in the Canon per se it seems unlikely to have been used in the same sense as we think of it, i.e. it's not a technical term. The Buddhist Hybrid Sanskrit Dictionary suggests that the Pāli equivalent is anāgariya. PED points to the entry for agāra/agāriya. Agāra (same in Sanskrit) just means 'house'. Under agāriya it notes that it is usually used in the (feminine) negative: 'anagāriyā'. It is used in the context of going forth (pabbajita) into the 'homeless' life - so is the same technical term (PED notes agāriya = agārika). An agārika is a layperson - i.e. someone who dwells in a house (as opposed to a paribbājaka or vagrant).
samyak/mithyā (Pāli sammā/micchā)
This pair of adjectives find frequent use in Buddhist terminology. For instance there is samyagdṛṣṭi (P. sammādiṭṭhi) and mithyādṛṣṭi (P. micchādiṭṭhi), that is right-view and wrong-view. Samyak/samyag are forms demanded by sandhi, and the base form of the word is samyañc. The root here is √añc 'to bend'. The prefix saṃ- here makes it mean 'to bend with', and the 'y' being a euphonic insertion. In common parlance we might even say that it means 'to go with the flow or grain'. There is an applied meaning which is to pay respects to - i.e. to bow to or with. I often think that Indian metaphors owe a lot to the early Indo-Europeans having lived in places where rivers where very important. Samyañc 'to bend with' comes to mean, via bending the right way, or going with the natural order, 'correct, right' and perhaps even 'perfect' (i.e. getting everything right). Mithyā on the other hand is a contracted form of mithūyā and means 'inverted', or 'contrary'. The root here is √mith meaning both to 'alternate' and to 'altercate' (a nice summing up by William Dwight Whitney!) From this root we get the indeclinable particle mithu which indicates 'an alternate', or some kind of conflict; as well as similar sounding word, mithuna, meaning 'a pair'. So samyakdṛṣṭi means 'to have a world-view which is in accordance with the natural order; to be seeing things as they are'; while mithyādṛṣṭi means ' to have a world-view which is contrary to how things are, which goes against the grain'.