Merriam-Webster's Collegiate® Dictionary, 11th Edition
SPARE
I. verb (spared; sparing)
Etymology: Middle English, from Old English sparian; akin to Old High German sparōn to spare, Old English spær, adjective , scant Date: before 12th century transitive verb to forbear to destroy, punish, or harm, to refrain from attacking or reprimanding with necessary or salutary severity, to relieve of the necessity of doing or undergoing something , to refrain from ; avoid , to use or dispense frugally,
6. to give up as not strictly needed , to have left over or as margin , intransitive verb to be frugal, to refrain from doing harm, spareable adjective sparer noun
II. adjective (sparer; sparest)
Etymology: Middle English, from Old English spær sparing, scant; akin to Old High German spar spare
Date: 14th century
not being used, being over and above what is needed ; superfluous , not liberal or profuse ; sparing , healthily lean, not abundant or plentiful, see: lean sparely adverb spareness noun
III. noun
Date: 1907
1. a spare tire, a duplicate (as a key or a machine part) kept in reserve, the knocking down of all 10 pins with the first 2 balls in a frame in bowling