The Collaborative International Dictionary of English v.0.48:

Mousy \Mous"y\ (mouz"[y^]), a.
   Infested with mice; smelling of mice.
   [1913 Webster]

WordNet (r) 3.0 (2006):

mousy
    adj 1: quiet and timid and ineffectual [syn: mousy, mousey]
    2: infested with mice [syn: mousy, mousey]
    3: of something having a drab pale brown color resembling a
       mouse; "a mousy brownish-grey color"; "mousy hair"; "mouse-
       colored hair" [syn: mousy, mousey, mouse-colored,
       mouselike]

Moby Thesaurus II by Grady Ward, 1.0:

161 Moby Thesaurus words for "mousy":
   Quaker-colored, acier, afraid, ashen, ashy, bashful, brown,
   brownish, canescent, chicken, chickenhearted, cinereous, cinerous,
   colorless, confused, conscious, coward, cowardly, cowed, cowering,
   coy, dapple, dapple-gray, dappled, dappled-gray, daunted, demure,
   diffident, dingy, dismal, dismayed, dove-colored, dove-gray, drab,
   dreary, dull, dun, dusty, echoless, fainthearted, fearful, fearing,
   fearsome, flat, funking, funky, glaucescent, glaucous, goosy, gray,
   gray-black, gray-brown, gray-colored, gray-drab, gray-green,
   gray-spotted, gray-toned, gray-white, grayed, grayish, grey,
   griseous, grizzle, grizzled, grizzly, henhearted, hush as death,
   hushed, in fear, inarticulate, inaudible, intimidated, iron-gray,
   jumpy, lead-gray, leaden, lily-livered, livid, milk-livered,
   milksoppish, milksoppy, mouse-colored, mouse-gray, mouselike,
   mousey, nervous, noiseless, overtimid, overtimorous, panic-prone,
   panicky, pearl, pearl-gray, pearly, pigeonhearted, plain,
   quiescent, quiet, rabbity, ratty, rodent, rodential, sad, scary,
   self-conscious, self-effacing, shaky, shamefaced, shamefast,
   shivery, shrinking, shy, silent, silver, silver-gray, silvered,
   silvery, sissified, sissy, skittery, skittish, slate-colored,
   slaty, smoke-gray, smoky, sober, soft, somber, soundless,
   stammering, startlish, steel-gray, steely, still, still as death,
   stilly, stone-colored, subaudible, taupe, timid, timorous,
   trembling, tremulous, trepidant, trigger-happy, unarticulated,
   unhearable, unmanly, unmanned, unpronounced, unsounded, unuttered,
   unvocalized, unvoiced, verminous, weak, weak-kneed, weakhearted,
   whist, white-livered, yellow