Feeling poorly, omit one (7)
I believe the answer is:
emotion
'feeling' is the definition.
(emotion is a kind of feeling)
'poorly omit one' is the wordplay.
'poorly' indicates an anagram (a poor spelling).
'omit'+'one'='omitone'
'omitone' is an anagram of 'EMOTION'.
(Other definitions for emotion that I've seen before include "sense" , "Surprise, perhaps" , "Feeling such as joy, sorrow and fear" , "Feeling like love or hate" , "Anger, perhaps" .)