second base
/ˌsɛk(ə)nd ˈbeɪs/noun
1 Baseball. The second of the four bases which the batter must touch in succession in order to score a run.
2 Slang (chiefly North American ). The second of four notional stages of sexual activity, usually characterized as the act of touching the breasts.
Origin
Mid 19th century; earliest use found in By-laws & Rules Knickerbocker Base Ball Club. From second + base.