Always, in poetry (3)
I believe the answer is:
eer
'always in poetry' is the definition.
(poetic version of 'ever')
This is all the clue.
(Other definitions for eer that I've seen before include "Always (poetical)" , "Always (poetic)" , "Ever poetically" , "Ever to the poet (3)." , "Before, poetically speaking (1'2)" .)