Substantially, I’ll say, tense agitation (11)
I believe the answer is:
essentially
'substantially' is the definition.
(thesaurus)
'i'll say tense agitation' is the wordplay.
'i'll say tense' can be anagrammed to 'ESSENTIALLY'.
However, I'm unsure how this is indicated.
Can you help me to learn more?
(Other definitions for essentially that I've seen before include "Basically" , "By its very nature" , "At heart" , "mainly" , "Fundamentally" .)