I say ring for the blessed commander! (7)
I believe the answer is:
halogen
'i say' is the definition.
(iodine - symbol 'I' - is an example)
'ring for the blessed commander' is the wordplay.
'ring for the blessed' becomes 'halo' (eg a saint might wear a halo).
'commander' becomes 'gen' (abbreviation for general).
'halo'+'gen'='HALOGEN'
(Other definitions for halogen that I've seen before include "Element such as iodine" , "Element like, eg, fluorine" , "I too maybe" , "I must be regarded as one" , "Eg, fluorine or chlorine" .)