Unfortunately they lack an opener (8)
I believe the answer is:
latchkey
'an opener' is the definition.
(I've seen this before)
'unfortunately they lack' is the wordplay.
'unfortunately' indicates an anagram (a bad or unfortunate spelling).
'they'+'lack'='theylack'
'theylack' is an anagram of 'LATCHKEY'.
(Other definitions for latchkey that I've seen before include "Common device to open outer door" , "Front door opener (for children with absent parents?)" , "Describes a child who returns to an empty home" , "Means of entry to (parentless?) house" , "A supposed freedom from domestic restrictions" .)