Season of which "vernal” is the related adjective (6)
I believe the answer is:
spring
'season' is the definition.
(spring is a season)
I cannot understand how the remainder of the clue works.
Can you help me to learn more?
(Other definitions for spring that I've seen before include "Source; help escape (from prison)" , "Well - bound" , "Bound < to get out of prison" , "Start season" , "Pounce -- pogo stick part" .)