"immaturest" in the adjective sense
1. immature
characteristic of a lack of maturity
"immature behavior"
2. young, immature
used of living things especially persons) in an early period of life or development or growth
"young people"
3. green, unripe, unripened, immature
not fully developed or mature not ripe
"unripe fruit"
"fried green tomatoes"
"green wood"
4. immature
not yet mature
5. unfledged, immature
of birds) not yet having developed feathers
"a small unfledged sparrow on the window sill"
Source: WordNet® (An amazing lexical database of English)
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