noun
An object or a person put in the rear or in the back of something to reinforce, hold, support.
A default arrangement that holds if all else fails.
(baseball) A wall or fence behind home plate.
(baseball, slang) A catcher; the position of catcher.
(rounders) The player who stands immediately behind the striking base.
(cricket, dated) The longstop.
(cricket, dated) The wicket-keeper.
(espionage) Something serving to bolster or support a cover story etc.
verb
(transitive) To serve as backstop for.
(transitive) To bolster, support.