Second president (5)
I believe the answer is:
adams
'second president' is the definition.
(John Adams, second president of the USA)
This is all the clue.
(Other definitions for adams that I've seen before include "Presidential father or son" , "Ansel --, US landscape photographer" , "John Quincy --, sixth US president" , "Father and son were American presidents" , "Richard --, Watership Down author" .)