Source : Webster's Revised Unabridged Dictionary (1913)

Slap \Slap\, n. [OE. slappe; akin to LG. slappe, G. schlappe;
   probably of imitative origin.]
   A blow, esp. one given with the open hand, or with something
   broad.

Slap \Slap\, v. t. [imp. & p. p. {Slapped}; p. pr. & vb. n.
   {Slapping}.]
   To strike with the open hand, or with something broad.

Slap \Slap\, adv. [Cf. LG. slap, G. schlapp. See {Slap}, n.]
   With a sudden and violent blow; hence, quickly; instantly;
   directly. [Colloq.] ``The railroad cars drive slap into the
   city.'' --Thackeray.

Source : WordNet®

slap
     n 1: a blow from a flat object (as an open hand) [syn: {smack}]
     2: the act of smacking something; a blow delivered with an open
        hand [syn: {smack}, {smacking}]
     [also: {slapping}, {slapped}]

slap
     adv : directly; "he ran bang into the pole"; "ran slap into her"
           [syn: {bang}, {slapdash}, {smack}, {bolt}]
     [also: {slapping}, {slapped}]

slap
     v : hit with something flat, like a paddle or the open hand;
         "The impatient teacher slapped the student"; "a gunshot
         slapped him on the forehead"
     [also: {slapping}, {slapped}]