Oregon provided diamonds for opening (7)
I believe the answer is:
orifice
'opening' is the definition.
(synonyms)
'oregon provided diamonds' is the wordplay.
'oregon' becomes 'or'.
'provided' becomes 'if' (eg 'provided it's sunny' means 'if it's sunny').
'diamonds' becomes 'ice' (slang term for diamonds).
'or'+'if'+'ice'='ORIFICE'
'for' acts as a link.
(Other definitions for orifice that I've seen before include "Vent" , "For CIE, I look for an opening" , "Mouth-like opening" , "Hole, opening" , "provided by gold and diamonds" .)