First institute established by nobleman (8)
I believe the answer is:
earliest
'first' is the definition.
(similar in meaning)
'institute established by nobleman' is the wordplay.
'institute' becomes 'i' (common abbreviation as in MIT).
'established' becomes 'est' (abbreviated used in shop signs).
'by' is a charade indicator (letters next to each other).
'nobleman' becomes 'earl' (earl is a kind of nobleman).
'i'+'est'='iest'
'iest' put after 'earl' is 'EARLIEST'.
(Other definitions for earliest that I've seen before include "Next available" , "Original or most previous" , "Very first in a sterile manner" , "Arriving first" , "Ateliers (anag.)" .)