Languor (9)
I believe the answer is:
lassitude
'languor' is the definition.
(I know that languor can be written as lassitude)
This is the entire clue.
(Other definitions for lassitude that I've seen before include "Listlessness, lethargy" , "Weakness" , "30 [LETHARGY]" , "Is saluted with tiredness" , "slackness" .)