swallow
鳦 refers specifically to a swallow, the bird.
鳦 combines 鳥 (bird) with 乙, which likely serves as a phonetic component. The exact historical development is uncertain.
A bird 鳥 with a curved stroke 乙 beside it: picture a swallow's distinctive forked tail or swift, curved flight path.
For イツ, imagine a swallow that eats insects: 'eats' -> イツ, and the bird catches bugs in mid-air.