Wife in love, remarkably I say (5)
I believe the answer is:
vowel
'i say' is the definition.
(I is a vowel)
'wife in love remarkably' is the wordplay.
'wife' becomes 'w'.
'in' indicates putting letters inside.
'remarkably' is an anagram indicator.
'love' is an anagram of 'voel'.
'w' inserted within 'voel' is 'VOWEL'.
(Other definitions for vowel that I've seen before include "aeio or u" , "Open sound in speech" , "Possibly a" , "E.g. A, but not B" , "Type of letter such as A" .)