a slap on the back Definition

slap
noun

1. A blow with the palm of the hand or anything flat.

Thesaurus: smack, whack, blow, wallop, cuff, clap.
2. The sound made by such a blow, or by the impact of one flat surface with another.
3. A snub or rebuke.

verb slapped, slapping

1. To strike with the open hand or anything flat.

Thesaurus: hit, strike, spank, whack, pat, clout, clobber, paw.
2. To bring or send with a slapping sound.

Example: He slapped the newspaper down on the table
3. colloq
To apply thickly and carelessly.
Example: She quickly slapped make-up on her face
Form: slap something on (often)
4. colloq
To reject or contradict them abruptly; to rebuke them.
Form: slap someone down (often)

adverb

colloq:
1. Exactly or precisely.

Example: slap in the middle
2. Heavily or suddenly; with a slap.

Example: He fell slap on his face

Idiom: a slap in the face

colloq
An insult or rebuff.
Thesaurus: insult, affront, rebuke, indignity, offence.

Idiom: a slap on the back

colloq
Congratulations.

Idiom: a slap on the wrist

colloq, often facetious
A mild reprimand.

Etymology: 17c: from German dialect slapp.