Greek character concerned with group turning up in stand (8)
I believe the answer is:
tolerate
'stand' is the definition.
('tolerate' can be a synonym of 'stand')
'greek character concerned with group turning up' is the wordplay.
'greek character' becomes 'eta' (letter from the Greek alphabet).
'concerned with' becomes 're'.
'group' becomes 'lot' (lot is a kind of group**).
'turning up' says the letters should be written in reverse.
'eta'+'re'+'lot'='etarelot'
'etarelot' reversed gives 'TOLERATE'.
'in' acts as a link.
(Other definitions for tolerate that I've seen before include "Put up with, permit without protest" , "Suffer" , "Turn a blind eye to" , "Endure, put up with" , "Put up with, bear" .)