Greek
i) ONTOLOGY: ‘the study of being and the essence or defining core of things’. Technically, the word comes from late Latin ontologia, which first appeared in the 1600s. ‘Ontology’ itself, according to the OED, first appeared in 1664, used by Gideon Harvey. However, ultimately the root of the word is Greek:
ὀντος - being
λογος - word, study of
(-logy a suffix we have met several times before)
ii) OENOPHILE: this is perhaps a bit of a cheat (but who cares because it is such a good word), as it is technically a transliteration that has been slightly anglicized. A ‘wine-lover’. The Greek word breaks down as follows:
οἶνον - wine
φιλος - lover
It literally means ‘lover of wine’. Interestingly, οἶνον is believed to be related to the Latin ‘VINUM’. The connection may be as follows. One school of thought argues that the ‘V’ in Latin was in fact ONCE pronounced as a ‘W’ sound, with the ‘V’ pronunciation arriving in later Latin. In Greek, there was once a letter called the digamma (Ϝ/ϝ) (names because it looks like a double capital gamma), actually called ‘wau’, likely being pronounced as a ‘W’. οἶνον may well have originally begun with the digamma. So
VINUM as WINUM
οἶνον as Ϝοἶνον (woinon)
The link, thus, becomes rather clearer.
iii) OPTHALMOLOGY: the area of medicine related to care of the ‘eyes’. Once again, we meet the ‘-logy’ suffix. The first part comes from the Greek ὀφθαλμος, meaning eye.
Latin
i) OBLIVIOUS: ‘not aware of or concerned with what is going on around one’. The word comes from ‘obliviosus’, meaning ‘forgetful’. The related verb is ‘obliviscor, oblivisci, oblitus sum’, meaning ‘to forget, be forgetful of’.
ii) OBVIOUS: ‘plain, clear to see, readily apparent’. The word comes from the Latin ‘obvius’ meaning ‘that which is in the way, exposed, open’.
An Interesting Case
This derivative does not begin with an ‘o’, but the original does.
The word is ECONOMICS, the study of the production, distribution, and usage of human resources. It comes from the Greek word, ‘οἰκονομια’.
οἰκος - household
-νομια from νῶμαω - direct, manage
Greek also had the verb ‘οἰκονομεω’ – ‘to manage a household, arrange, distribute’.
This may seem rather different to the meaning we attach to ‘ECONOMICS’ nowadays. But the principle of management, allocation of resources has stayed exactly the same.