1792, agent noun from equalize. Sports sense attested by 1930; in the U.S. underworld slang sense of "pistol," it is from c. 1900.
Entries linking to equalizer
equalize v.
1580s, "make equal, cause to be equal in amount or degree," from equal (adj.) + -ize. Sports score sense attested by 1925. Related: Equalized; equalizing.