Nearly let out for evermore (9)
I believe the answer is:
eternally
'evermore' is the definition.
('eternally' can be a synonym of 'evermore')
'nearly let out' is the wordplay.
'out' is an anagram indicator (out can mean wrong or inaccurate).
'nearly'+'let'='nearlylet'
'nearlylet' anagrammed gives 'ETERNALLY'.
'for' is the link.
(Other definitions for eternally that I've seen before include "Always and ever" , "constantly" , "For evermore" , "Always and forever" , "all the time" .)