Wiktionary
unadoptable
a. That cannot be adopted; unsuitable for adoption.
WordNet
unadoptable
adj. difficult to place in an adoptive home [ant: adoptable]
Usage examples of "unadoptable".
They were hopeless unadoptable children with terrible birth defects, but every one of them had a healthy young brain.
By aligning herself with a speechless, damaged brother, she made herself unadoptable, unplaceable.
Eight months old, severely handicapped, and born with a heart defect, Jane was labeled unadoptable by Social Services and the nurses at the hospital where Alessandra did fund-raising volunteer work.