Everyone in trial, most lofty (7)
I believe the answer is:
tallest
'most lofty' is the definition.
('tall' can be a synonym of 'lofty')
'everyone in trial' is the wordplay.
'everyone' becomes 'all' (all people).
'in' means one lot of letters goes inside another.
'trial' becomes 'test' (synonyms).
'all' put inside 'test' is 'TALLEST'.
(Other definitions for tallest that I've seen before include "most unlikely" , "most exaggerated" , "most implausible" , "highest standing" , "Top out" .)