shotgun wedding

WordReference Random House Unabridged Dictionary of American English © 2025

shot′gun wed′ding, 

1. a wedding occasioned or precipitated by pregnancy.
2. Informal Terms a compromise, merger, accord, etc., occasioned by necessity:
   The coalition government was obviously a shotgun wedding.
Also, shot′gun mar′riage. 
• 1925–30, American.

Collins Concise English Dictionary © HarperCollins Publishers::

shotgun wedding noun

1. a wedding into which one or both partners are coerced, usually because the woman is pregnant