'nectarivorous' originates from Latin/Greek elements: 'nectar' (from Greek néktar, taken into Latin as 'nectar') and the combining form '-vorous' from Latin 'vorare' meaning 'to devour', with an inserted connecting vowel '-i-'.

'nectar' came into English via Latin from Greek 'néktar'; the suffix '-vorous' derives from Latin 'vorare' and Late Latin/Medieval Latin adjectival formations (e.g. '-vorus'), and the modern English adjective 'nectarivorous' was formed by combining these elements.

Initially the elements meant 'nectar' and 'to devour'; the combined adjective has meant 'feeding on nectar' since its formation and has retained that specific biological sense.