A top year, with King throttled at an early stage (7)
I believe the answer is:
already
'throttled at an early stage' is the definition.
I can't judge whether this defines the answer.
'a top year with king' is the wordplay.
'top' becomes 'lead' (both can mean 'most important').
'year' becomes 'y'.
'with' is an insertion indicator.
'king' becomes 'R' (abbreviation of Latin rex).
'lead'+'y'='leady'
'leady' enclosing 'r' is 'lready'.
'a'+'lready'='ALREADY'
Can you help me to learn more?
(Other definitions for already that I've seen before include "As early as this, so soon?" , "thus far" , "By the time in question" , "Previously" , "earlier than might have been expected" .)