Watchful for a later change (5)
I believe the answer is:
alert
'watchful' is the definition.
(similar in meaning)
'later change' is the wordplay.
'change' indicates anagramming the letters.
'later' is an anagram of 'ALERT'.
'for a' is the link.
(Other definitions for alert that I've seen before include "Vigilant, watchful" , "Wide awake and watchful" , "In state of watchfulness" , "Put on guard, warn" , "Warning signal" .)