Man let out is keen (6)
I believe the answer is:
lament
'keen' is the definition.
(keen can mean to wail with grief)
'man let out' is the wordplay.
'out' is an anagram indicator (out can mean wrong or inaccurate).
'man'+'let'='manlet'
'manlet' anagrammed gives 'LAMENT'.
'is' is the link.
(Other definitions for lament that I've seen before include "requiem" , "Expr. of grief; mourn" , "Dirge; bewail" , "Mourn (a person's death)" , "Express disappointment" .)