hear it again

: to listen secretly to private conversation

Example sentence:
"I didn't mean to eavesdrop," said Darla apologetically, "but I overheard you say you're planning a surprise party for Kate and I wondered if I could help."

Etymology:
The verb "eavesdrop" developed from the even older noun "eavesdropper."
Imagine that you're a medieval knight trying to find out if a royal visitor is plotting against the queen. He's in a locked, guarded room. Where could you hide to listen to his conversations to see if he's up to no good? Under the eaves, the part of a roof that hangs out over the outside walls and shelters the windows and doors from rain running off the roof. An eavesdropper was literally someone who stood under the eaves to hear a conversation inside. The first eavesdroppers may simply have been trying to stay dry and accidentally overheard conversations, but later eavesdroppers were surely listening on purpose.