Omit one accidentally showing strong feeling (7)
I believe the answer is:
emotion
'strong feeling' is the definition.
(I've seen this before)
'omit one accidentally' is the wordplay.
'accidentally' indicates an anagram (a chaotic or accidental ordering of the letters).
'omit'+'one'='omitone'
'omitone' with letters rearranged gives 'EMOTION'.
'showing' is the link.
(Other definitions for emotion that I've seen before include "E.g. fear, hate etc." , "Strong desire" , "sense" , "Feeling, say love or hate" , "Anger, perhaps" .)