Pat1  —v. (-tt-) 1 strike gently with a flat palm, esp. In affection, sympathy, etc. 2 flatten or mould by patting. —n. 1 light stroke or tap, esp. With the hand in affection etc. 2 sound made by this. 3 small mass (esp. Of butter) formed by patting.  pat on the back congratulatory gesture. [probably imitative]