The Collaborative International Dictionary of English v.0.48:

Girlish \Girl"ish\, a.
   Like, or characteristic of, a girl; of or pertaining to
   girlhood; innocent; artless; immature; weak; as, girlish
   ways; girlish grief. -- Girl"ish*ly, adv. --
   Girl"ish*ness, n.
   [1913 Webster]

WordNet (r) 3.0 (2006):

girlish
    adj 1: befitting or characteristic of a young girl; "girlish
           charm"; "a dress too schoolgirlish for office wear" [syn:
           girlish, schoolgirlish]

Moby Thesaurus II by Grady Ward, 1.0:

82 Moby Thesaurus words for "girlish":
   airy, attenuate, attenuated, beardless, boyish, boylike, calflike,
   childish, childlike, coltish, delicate, diaphanous, diluted,
   distaff, ethereal, female, feminine, fine, fine-drawn, finespun,
   flimsy, frail, gauzy, gentlewomanlike, girllike, gossamer, gracile,
   gynecic, gynecoid, gynic, insubstantial, kiddish, kittenish, lacy,
   ladylike, light, little-girlish, maiden, maidenly, matronal,
   matronlike, matronly, misty, muliebral, papery, petticoat, puerile,
   puplike, puppyish, puppylike, rare, rarefied, slender, slenderish,
   slight, slight-made, slim, slimmish, slinky, small, subtle, svelte,
   sylphlike, tenuous, thin, thin-bodied, thin-set, thin-spun,
   thinnish, threadlike, vague, wasp-waisted, watered, watered-down,
   watery, weak, willowy, wiredrawn, wispy, womanish, womanlike,
   womanly