only son

only son (plural only sons)

1. A sole male child, whether one among multiple siblings, or one who has no siblings.
   • 1991 November 18, Alessandra Stanley, “The Symbols Spawned by a Killing”, in New York Times:

     Mr. Doyle, an only son, grew up with the undivided attention of affectionate parents and two doting sisters.

2. Used other than figuratively or idiomatically: see only,‎ son.

   He was the only son to go to college.

• only child
• only daughter