slap, smack -- (a blow from a flat object (as an open hand))
smack, smacking, slap -- (the act of smacking something; a blow delivered with an open hand)
Overview of verb slap
The verb slap has 1 sense
slap -- (hit with something flat, like a paddle or the open hand; "The impatient teacher slapped the student"; "a gunshot slapped him on the forehead")
Overview of adv slap
The adv slap has 1 sense
bang, slap, slapdash, smack, bolt -- (directly; "he ran bang into the pole"; "ran slap into her")