Messenger over time becomes royal attendant (8)
I believe the answer is:
courtier
'royal attendant' is the definition.
(I've seen this before)
'messenger over time' is the wordplay.
'messenger' becomes 'courier' (synonyms).
'over' indicates putting letters inside.
'time' becomes 't' (abbreviation).
'courier' enclosing 't' is 'COURTIER'.
'becomes' acts as a link.
(Other definitions for courtier that I've seen before include "Attendant on monarch" , "who has Palace role?" , "Sovereign's attendant" , "Messenger" , "Palace hanger-on" .)