Source : Webster's Revised Unabridged Dictionary (1913)

Immature \Im`ma*ture"\, a. [L. immaturus; pref. im- not +
   maturus mature, ripe. See {Mature}.]
   1. Not mature; unripe; not arrived at perfection of full
      development; crude; unfinished; as, immature fruit;
      immature character; immature plans. ``An ill-measured and
      immature counsel.'' --Bacon.

   2. Premature; untimely; too early; as, an immature death.
      [R.] --Jer. Taylor.

Source : WordNet®

immature
     adj 1: characteristic of a lack of maturity; "immature behavior"
            [ant: {mature}]
     2: lacking in development; "immature plans"; "an unformed
        character" [syn: {unformed}]
     3: (used of living things especially persons) in an early
        period of life or development or growth; "young people"
        [syn: {young}] [ant: {old}]
     4: not fully developed or mature; not ripe; "unripe fruit";
        "fried green tomatoes"; "green wood" [syn: {green}, {unripe},
         {unripened}] [ant: {ripe}]
     5: not yet mature [ant: {mature}]
     6: (of birds) not yet having developed feathers; "a small
        unfledged sparrow on the window sill" [syn: {unfledged}]
        [ant: {fledged}]