The Collaborative International Dictionary of English v.0.48:

Dotty \Dot"ty\, a. [From 2d Dot.]
   1. Composed of, or characterized by, dots.
      [Webster 1913 Suppl.]

   2. [Perh. a different word; cf. Totty.] Unsteady in gait;
      hence, feeble; half-witted. [Eng.]
      [Webster 1913 Suppl.]

WordNet (r) 3.0 (2006):

dotty
    adj 1: informal or slang terms for mentally irregular; "it used
           to drive my husband balmy" [syn: balmy, barmy,
           bats, batty, bonkers, buggy, cracked,
           crackers, daft, dotty, fruity, haywire,
           kooky, kookie, loco, loony, loopy, nuts,
           nutty, round the bend, around the bend, wacky,
           whacky]
    2: intensely enthusiastic about or preoccupied with; "crazy
       about cars and racing"; "he is potty about her" [syn:
       crazy, wild, dotty, gaga]

Moby Thesaurus II by Grady Ward, 1.0:

112 Moby Thesaurus words for "dotty":
   abnormal, absurd, anomalous, balmy, bananas, barmy, bats, batty,
   beany, besotted, bespangled, blotched, blotchy, bonkers, buggy,
   bughouse, bugs, crackers, crank, crankish, cranky, crazy,
   crotchety, cuckoo, daffy, deviant, deviative, different, dippy,
   divergent, dotted, eccentric, enamored, erratic, exceptional,
   fantastic, fey, flaky, flea-bitten, flecked, fleckered, flipped,
   freaked-out, freakish, frecked, freckled, freckly, fruitcakey,
   fruity, funny, gaga, goofy, haywire, idiocratic, idiosyncratic,
   infatuate, insane, irregular, just plain nuts, kinky, kooky, loony,
   loopy, macular, maculate, maculated, maggoty, nuts, nutty, odd,
   oddball, off the hinges, off the track, off the wall, patchy,
   peculiar, peppered, pocked, pockmarked, pocky, pointille,
   pointillistic, polka-dot, potty, preposterous, punctated, queer,
   quirky, round the bend, screwball, screwballs, screwy, singular,
   slaphappy, spangled, specked, speckled, speckledy, speckly,
   splotched, splotchy, spotted, spotty, sprinkled, stippled, strange,
   studded, twisted, unconventional, unnatural, wacky, whimsical