Every variety of ache (4)
I believe the answer is:
each
'every' is the definition.
(synonyms)
'variety of ache' is the wordplay.
'variety of' indicates an anagram.
'ache' is an anagram of 'EACH'.
(Other definitions for each that I've seen before include "This way for a place" , "Per person" , "Every - apiece" , "every one of a group" , "Every single one, person or thing" .)