Popular admiral oddly overlooked NATO letter (5)
I believe the answer is:
india
'nato letter' is the definition.
(NATO phonetic alphabet)
'popular admiral oddly overlooked' is the wordplay.
'popular' becomes 'in' ('in' can mean trendy).
'oddly overlooked' indicates alternate letters (letters in odd-numbered positions removed).
The alternating letters of 'admiral' are 'dia'.
'in'+'dia'='INDIA'
(Other definitions for india that I've seen before include "I identified on radio" , "home to her Mumbai family" , "One preceding Juliet" , "vast country" , "In aid, strangely, of the country" .)