- a horse that bolts, or runs away
- a person who withdraws from a political party, group, etc.
- A horse given to bolting.
- One who gives up membership in or withdraws support from a political party.
- A machine used for sifting, especially for sifting flour.
- One who operates a sifting machine.
- A person or thing that bolts, or runs suddenly.
- (botany, horticulture) A plant that grows larger and more rapidly than usual.
- (flour milling) A machine or mechanism that automatically sifts milled flour.
- A person who sifts flour or meal.
- (petroleum refining) A filter mechanism.
- (Australia, sports) An obscure athlete who wins an upset victory.
- (Australia, horseracing) A horse that wins at long odds.
- (New Zealand, sports) In team sports, a relatively little-known or inexperienced player who inspires the team to greater success.
- (US, politics) A member of a political party who does not support the party's nominee.
- (military aviation) A missed landing on an aircraft carrier; an aircraft that has made a missed landing.
- A kind of fishing line; a boulter.
From bolt + -er.