Sets the seal on many measures (8)
I believe the answer is:
clinches
'sets' is the definition.
The answer and definition can be both acts as well as being plural nouns.
Perhaps you can see a link between them that I can't see?
'seal on many measures' is the wordplay.
'seal' becomes 'clinch' (I've seen this before).
'on' is a charade indicator (letters next to each other) (in a down clue, letters appear on others).
'many measures' becomes 'es' (e is a kind of measure. I am not sure about the 'many' bit.).
'clinch'+'es'='CLINCHES'
'the' is the link.
Can you help me to learn more?
(Other definitions for clinches that I've seen before include "finally settles" , "Tight or amorous embraces, in the boxing ring" , "Tight grips in boxing" .)