The word "spare" has a number of synonyms that can be used in different contexts. For example, the word "extra" is often used to refer to something that is in addition to what is needed or expected. Similarly, the word "surplus" can be used to describe something that is in excess of what is needed or required. Another synonym for "spare" is "unused", which refers to something that is not being used at the moment. Other synonyms for "spare" include "backup", "reserve", "additional", "excessive", and "unoccupied". Depending on the context, any of these words can be used to convey different shades of meaning.