Moan about a lady on vacation — something not quite right? (7)
I believe the answer is:
anomaly
'something not quite right?' is the definition.
(an anomaly is something unusual or wrong)
'moan about a lady on vacation' is the wordplay.
'about' indicates anagramming the letters.
'on vacation' says to hollow out the word (remove centre letters).
'lady' with its centre taken out is 'ly'.
'moan' anagrammed gives 'anom'.
'anom'+'a'+'ly'='ANOMALY'
(Other definitions for anomaly that I've seen before include "There's curiosity" , "Something deviating from the usual" , "Something irregular" , "Irregular result" , "It turns up irregularly" .)