Mark to introduce the Spanish officer (7)
I believe the answer is:
colonel
'officer' is the definition.
(colonel is a kind of officer)
'mark to introduce the spanish' is the wordplay.
'mark' becomes 'colon' (colon is a kind of mark).
'to introduce' means one lot of letters go next to another.
'the spanish' becomes 'el' ('the' in Spanish).
'colon'+'el'='COLONEL'
(Other definitions for colonel that I've seen before include "Commissioned officer" , "Comissioned military officer" , "Army officer ranking below a brigadier" , "Army rank" , "'No cello for this officer, strangely (7)'" .)