You use spare to describe something that is the same as things that you are already using, but that you do not need yet and are keeping ready in case another one is needed.
You use spare to describe something that is not being used by anyone, and is therefore available for someone to use.
If you have something such as time, money, or space to spare, you have some extra time, money, or space that you have not used or which you do not need.
If you spare time or another resource for a particular purpose, you make it available for that purpose.
If a person or a place is spared, they are not harmed, even though other people or places have been.
If you spare someone an unpleasant experience, you prevent them from suffering it.
Someone who is described as spare is tall and not at all fat.
Something such as a room that is spare is very plain with no unnecessary features.
9. see also: sparing
If you spare no effort in doing something, you do it as well as possible, without worrying about the amount of work involved. If you spare no expense in doing it, you do it as well as possible, without trying to save money.
If you spare a thought for an unfortunate person, you make an effort to think sympathetically about them and their bad luck.
12. to spare someone's blushes -> see blush