eavesdrop
Concise Oxford English Dictionary © 2008 Oxford University Press:
eavesdrop/ˈiːvzdrɒp/
▶verb (eavesdrops, eavesdropping, eavesdropped) secretly listen to a conversation.
– derivatives
eavesdropper noun.
eavesdropper noun.
– origin C17: back-form. from eavesdropper (ME), from the obs. noun eavesdrop ‘the ground on to which water drips from the eaves’, prob. from ON upsardropi.
'eavesdrop' also found in these Oxford entries:

