adjectives
thin and fit
"the spare figure of a marathon runner"; "a body kept trim by exercise"
more than is needed, desired, or required
"trying to lose excess weight"; "found some extra change lying on the dresser"; "yet another book on heraldry might be thought redundant"; "skills made redundant by technological advance"; "sleeping in the spare room"; "supernumerary ornamentation"; "it was supererogatory of her to gloat"; "delete superfluous (or unnecessary) words"; "extra ribs as well as other supernumerary internal parts"; "surplus cheese distributed to the needy"
not taken up by scheduled activities
"a free hour between classes"; "spare time on my hands"
kept in reserve especially for emergency use
"a reserve supply of food"; "a spare tire"; "spare parts"
is similar to
not necessary
lacking in amplitude or quantity
"a bare livelihood"; "a scanty harvest"; "a spare diet"
lacking embellishment or ornamentation
"a plain hair style"; "unembellished white walls"; "functional architecture featuring stark unornamented concrete"