Entry 3 senses · 2 variants Webster, 1913 Slapper · Slap·per · IPA /ˈslæpɚ/ n. a. 01 n. One who, or that which, slaps. 1. One who, or that which, slaps. 2. Anything monstrous; a whopper.[Slang] 02 a. Very large; monstrous; big. 1. Very large; monstrous; big.[Slang.]