border-security
catatonic
foolproof
frictionless
inaudible
indistinguishable
insentient
lipless
no-one
nose-to-nose
numinous
screw-threaded
sound-proof
soundproof
speckless
unaltered
undetectable
uneatable
uninhabitable
unnoticeable
unobtainable
unrecognisable
unrecognizable
unsalable
weightless