useless
functionless
impractical
in disrepair
inapplicable
inoperable
inoperative
nonfunctional
nonutilitarian
otiose
out of order
out of whack
unconducive
unemployable
unfit
unhelpful
unserviceable
unsuitable
unworkable
destructible
error-free
foolproof
illegible
inefficacious
nonexistent
soundproof
sub-standard
unavailable
undamaged
undependable
undetectable
uninformative
uninhabitable
unneeded
unnoticeable
unobtainable
unrecognisable
unrecognizable
untenanted
untouchable
untraceable
excusable
fusible
inexcusable
reusable
usable