ˌtit for ˈtat BrE AmE noun [uncountable]
[ Date: 1500-1600 ; Origin: Probably from tip for tap 'tit for tat' (1500-1600) , from tip 'light blow' ( ⇨ ↑ tip 1 ) and tap 'light blow' ]
informal something bad that you do to someone because they have done something bad to you