A person who eavesdrops; someone who secretly listens to private conversations.
From 'eardrop' + '-er,' but the word originally derived from 'eavesdrop' (from 'eaves' of a house + 'drop' of water). 'Eardropper' is a folk etymology variation that shows how people understood the word.
Eavesdroppers were supposedly people who stood under the eaves (dripping edge) of houses to listen through windows—and 'eardropper' shows how people tried to make sense of this funny old word by connecting it to 'ear' instead of 'eaves'!
Complete word intelligence in one call. Free tier — 50 lookups/day.