1873, "fondling, indulgence," verbal noun from pet (v.). Meaning "amorous caressing, foreplay" is from 1920 (in F. Scott Fitzgerald).
Entries linking to petting
pet v.
1620s, "treat as a pet," from pet (n.1). Sense of "to stroke" is first found 1818. Slang sense of "kiss and caress" is from 1920 (implied in petting). Related: Petted.