1) Beat 2) Blow 3) Bop 4) Hit 5) Punch 6) Swat 1) Blow 2) Deliver a hard blow to 3) Hit with a paddle 4) Hitting sound 5) Impact noise 6) Mega-hit 7) Sharp blow 8) Sharp impact sound 9) Smack with a book 10) Sound of a hit 11) Sound of a sharp blow 12) To beat 13) To fill to overflow 14) To hit with a flat implement 
• (v. t.) To fill to overflow. • (v. t.) To strike with something flat or heavy; to bang, or thrash: to thump. • (n.) A heavy blow with something flat or heavy; a thump.
Thwack (thwăk) transitive verb [ imperfect & past participle Thwacked ; present participle & verbal noun Thwacking .] [ Confer Middle English thakken to stroke, Anglo-Saxon þaccian , English whack .] 1...Thwack noun A heavy blow with something flat or heavy; a thump. « With many a stiff thwack , many a bang, Hard crab tree and old iron rang.» Hudibras. 
[n] - a hard blow with a flat object
verb deliver a hard blow to; `The teacher smacked the student who had misbehaved` noun a hard blow with a flat object