inconspicuous
insignificant
invisible
undistinguished
inobservable
unobservable
unobtrusive
bedridden
catatonic
foolproof
frictionless
geniculate
non-existing
nose-to-nose
pitch-black
single-handed
soundproof
undefended
undetectable
undistinguishable
uninhabitable
unobtainable
unopposed
unrecognisable
unrecognizable
unremarked
unusable
word-for-word
conspicuous