long ears; gossiper
Literally 'rabbit ears'. Idiomatically refers to a person who has sharp hearing for gossip or secrets, akin to 'having big ears' in English.
He's a gossiper, so be careful with secrets.
That person has big ears and spreads rumors quickly.
Compound of 兎 (usagi, 'rabbit') and 耳 (mimi, 'ear'). The idiomatic sense likely derives from the image of a rabbit's long ears catching sounds from afar.