spare
n. countablen. an extra item that you keep in case you lose or break the one you are using. You might keep one in your car or your bag for emergencies.
n. an item kept in reserve as a replacement for one that is lost, broken, or exhausted. Often used in the context of mechanical parts or household essentials.
I always keep a spare in the trunk of my car.
The mechanic checked the tire and realized the driver didn't have a spare in the back.
While the primary generator is robust, the facility maintains a high-capacity spare to ensure that critical systems remain operational during a prolonged power outage.
From Middle English spare, spar, from Old English spær (“sparing, scant”), from Proto-Germanic sparaz, from Proto-Indo-European sph₁rós, from the root *speh₁-. Compare Dutch spaar(zaam), German spar(sam) and spär(lich), Swedish spar(sam), Icelandic sparr (“sparing”); also Latin (pro)sperus (“lucky”), Old Church Slavonic споръ (sporŭ, “plentiful”), Albanian shperr (“earn money”), Persian سپار (sepâr, “entrust; deposit”), Ancient Greek σπαρνός (sparnós, “rare”), Sanskrit स्फिर (sphirá, “thick”).
From Middle English sparen, sparien, from Old English sparian (“to spare, show mercy to, refrain from injuring or destroying”), from Proto-Germanic sparōną, sparāną (“to save, keep, spare”), from Proto-Indo-European *sper- (“to be productive, earn”). Cognate with Scots spar, spare, spair (“to spare”), West Frisian sparje (“to save, spare”), Dutch sparen (“to save, spare”), German sparen (“to save, conserve, economise”), Swedish spara (“to save, save up”), Icelandic spara (“to save, conserve”).
Often used as a shorthand for 'spare tire' or 'spare key'.