Playmate

A playmate was a companion who someone would enjoyed playing or having fun with.

In 2377, while deprived of their memories and working at the Central Power Facility on Quarra, Tom Paris offered to introduce B'Elanna Torres to a couple who were expecting their first child soon, thinking she could find a playmate for her baby. (VOY: "Workforce")

In 2378, Q referred to Icheb as his son's little playmate, saying Junior might learn something if the boy died. (VOY: "Q2")

The term could also be used to describe a sexual partner. In 2369, Quark suggested Odo visit a holosuite, saying, "I could create a shape-shifter playmate for you. The two of you could intermingle." (DS9: "If Wishes Were Horses")