Syllable division derived from spelling — this word is not in the pronouncing dictionary, so no phonetic transcription is shown rather than a guessed one.
mid-nineties is a noun meaning "the time of life between 90 and 100". It carries one recorded sense.
the time of life between 90 and 100
Definitions, synonyms and semantic relations for mid-nineties come from Princeton University’s WordNet. Commonness is measured against a corpus of everyday English. Full sources and licences.