The Collaborative International Dictionary of English v.0.48:

Splenetic \Splen"e*tic\, a. [L. spleneticus: cf. F.
   spl['e]n['e]tique. See Spleen.]
   Affected with spleen; malicious; spiteful; peevish; fretful.
   "Splenetic guffaw." --G. Eliot.
   [1913 Webster]

         You humor me when I am sick;
         Why not when I am splenetic?             --Pope.
   [1913 Webster]

   Syn: Morese; gloomy; sullen; peevish; fretful.
        [1913 Webster]

The Collaborative International Dictionary of English v.0.48:

Splenetic \Splen"e*tic\, n.
   A person affected with spleen.
   [1913 Webster]

WordNet (r) 3.0 (2006):

splenetic
    adj 1: of or relating to the spleen [syn: splenic,
           splenetic, lienal]
    2: very irritable; "bristly exchanges between the White House
       and the press"; "he became prickly and spiteful"; "witty and
       waspish about his colleagues" [syn: bristly, prickly,
       splenetic, waspish]

Moby Thesaurus II by Grady Ward, 1.0:

85 Moby Thesaurus words for "splenetic":
   acerb, acerbate, acerbic, acid, acidic, acidulent, acidulous,
   acrimonious, adrenal, bearish, bitchy, bitter, blase, burning,
   cankered, cantankerous, caustic, choleric, churlish, crabbed,
   cranky, cross, cross-grained, crusty, cussed, disagreeable,
   dispirited, eccrine, embittered, endocrine, excitable, exocrine,
   fed-up, feisty, fractious, glandular, glandulous, gonadal,
   good and tired, holocrine, huffish, huffy, humoral, irascible,
   irked, irritable, jaded, life-weary, luteal, mean, melancholic,
   melancholy, merocrine, ornery, ovarian, pancreatic, perverse,
   prostatic, rancorous, rankled, resentful, resenting, satiated,
   sick, sick of, snappish, sore, spiteful, spleeny, stewing, testy,
   thymic, thyroidal, tired, tired of, tired of living,
   tired to death, ugly, virulent, waspish, wearied, weariful, weary,
   weary unto death, world-weary