also: あいたっ
interjection
An exclamation of sudden pain, equivalent to 'ouch' or 'ow'. Used in casual, spoken Japanese.
あいた！足をぶつけた。
Ouch! I bumped my foot.
あいたっ、注射が痛い。
Ow, the shot hurts.
Kanji spelling using 痛 (pain); rarely used in practice.
The adjective meaning 'painful'; あいた is the interjection derived from it, used as an exclamation.
Derived from the adjective 痛い (いたい, 'painful'), with the initial vowel lengthened for exclamatory effect.