They last out in secret (8)
I believe the answer is:
stealthy
'secret' is the definition.
(thesaurus)
'they last out' is the wordplay.
'out' indicates an anagram (out can mean wrong or inaccurate).
'they'+'last'='theylast'
'theylast' with letters rearranged gives 'STEALTHY'.
'in' acts as a link.
(Other definitions for stealthy that I've seen before include "Moving surreptitiously" , "Done in a quiet or secretive way" , "Covert - clandestine" , "Acting in quiet or secret way" , "That's Ely (anag.)" .)