Reticent about ester (5)
I believe the answer is:
terse
'reticent' is the definition.
Both the answer and definition are adjectives. Maybe they are linked in a way I don't understand?
'about ester' is the wordplay.
'about' is an anagram indicator.
'ester' with letters rearranged gives 'TERSE'.
Can you help me to learn more?
(Other definitions for terse that I've seen before include "Sparing with words; abrupt" , "Using few words" , "Short and sharp" , "Brusque and curt" , "Curt among trees" .)