Every single ache (4)
I believe the answer is:
each
'every single' is the definition.
(I've seen this before)
'ache' is the wordplay.
'ache' can be anagrammed to 'EACH'.
However, I'm not sure how this is indicated.
Can you help me to learn more?
(Other definitions for each that I've seen before include "...per head" , "Every - apiece" , "every individual" , "Singly, per capita" , "Ache (anag.)" .)