late 14c., twiteren, in reference to birds, of imitative origin (compare Old High German zwizziron, German zwitschern, Danish kvidre, Old Swedish kvitra). The noun meaning "condition of tremulous excitement" is attested from 1670s. The microblogging service with the 140-character limit was introduced in 2006. The following is considered an unrelated word of obscure origin:

TWITTER. 1. "That part of a thread that is spun too small." Yarn is said to be twined to twitters, when twined too small, S. Hence, to twitter yarn, to spin it unequally, A. Bor. Ray.

2. It is transferred to any person or thing that is slender or feeble. It is said of a lank delicate girl: "She is a mere twitter," S. [Jamieson, "Etymological Dictionary of the Scottish Language," Edinburgh, 1808]

1942, apparently first attested in the Walt Disney movie "Bambi" (there also was a song by that name but it was not in the studio release of the film), a past-participle adjective formed from twitter in the "tremulous excitement" noun sense (1670s) + pate (n.2) "head" (compare flutterpated, 1894).

Thumper: Why are they acting that way?

Friend Owl: Why, don't you know? They're twitterpated.

Flower, Bambi, Thumper: Twitterpated?

Friend Owl: Yes. Nearly everybody gets twitterpated in the springtime. For example: You're walking along, minding your own business. You're looking neither to the left, nor to the right, when all of a sudden you run smack into a pretty face. Woo-woo! You begin to get weak in the knees. Your head's in a whirl. And then you feel light as a feather, and before you know it, you're walking on air. And then you know what? You're knocked for a loop, and you completely lose your head!

Thumper: Gosh, that's awful.