Number of the Spanish flat (6)
I believe the answer is:
eleven
'number' is the definition.
(eleven is a kind of number)
'the spanish flat' is the wordplay.
'the spanish' becomes 'el' ('the' in Spanish).
'flat' becomes 'even' (level).
'el'+'even'='ELEVEN'
'of' is the link.
(Other definitions for eleven that I've seen before include "Not first team (6,6) - See 24" , "Bingo's "legs"?" , "football team, for example" , "Sporting side" , "Number, on a team perhaps" .)