1. adjective. Crazy
. But not violently dangerous or otherwise scarry crazy. Often means only that a person is a little odd
. Amusingly eccentric
, round the bend
, or wacky
. (We've got a lot of words for the half-way crazies). She's dotty!
2. adjective. Having a feeble or unsteady walk (especially animals); shaky, gimpy.
My horse is a bit dotty.
3. adjective. Obsessively infatuated. He's dotty over her.
Etymology: Probably from the Scottish dottle, meaning silly, which in turn comes from the Middle English doten, meaning to dote.
Thanks to Dictionary.com for the synonyms and etymology.