Opening for Irishman initially involved with diamonds (7)
I believe the answer is:
orifice
'opening' is the definition.
('orifice' can be a synonym of 'opening')
'for irishman initially involved with diamonds' is the wordplay.
'initially' suggests taking the first letters.
'involved' indicates anagramming the letters (involved can mean confusing or complex).
'with' is a charade indicator (letters next to each other).
'diamonds' becomes 'ice' (I've seen this before**).
The initial letter of 'irishman' is 'i'.
'for'+'i'='fori'
'fori' anagrammed gives 'orif'.
'orif'+'ice'='ORIFICE'
(Other definitions for orifice that I've seen before include "Vent" , "Finding opening" , "Mouth-like opening" , "8 [OPENING]" , "For CIE, I look for an opening" .)