Realism is lost in this field (5)
I believe the answer is:
realm
'this field' is the definition.
(synonyms)
'realism is lost' is the wordplay.
'lost' indicates named letters should be taken away.
'realism' with 'is' taken out is 'REALM'.
'in' acts as a link.
(Other definitions for realm that I've seen before include "the UK, perhaps" , "Province" , "Kingdom could be lamer" , "Kingdom, or field of activity" , "Kingdom, domain" .)