cavalry

noun4

1. •
   An individual unit of this arm of service.
2. •
   The branch of the military transported by fast light vehicles, also known as mechanized cavalry.
3. •
   (historical) The military arm of service that fights while riding horses.
4. •
   (figurative) A source of rescue, especially in an emergency.

   • "We landed in their killbox?" "We did. I am sor... No, belay that. Heads down! Cavalry incoming!" — 2015