The Collaborative International Dictionary of English v.0.48:

Jejune \Je*june"\, a. [L. jejunus fasting, hungry, dry, barren,
   scanty; of unknown origin.]
   [1913 Webster]
   1. Lacking matter; empty; void of substance.
      [1913 Webster]

   2. Void of interest; barren; meager; dry; as, a jejune
      narrative.

   3. Juvenile; childish; immature.
      [PJC]

   4. Lacking nutritional value.
      [PJC] - Je*june"ly, adv. -- Je*june"ness, n. --Bacon.
      [1913 Webster]

WordNet (r) 3.0 (2006):

jejunely
    adv 1: in an immature manner; "his teenage son still behaves
           very immaturely" [syn: immaturely, jejunely] [ant:
           maturely]