Fast turning the Spanish mad (6)
I believe the answer is:
stable
'fast' is the definition.
(fast can mean secure)
'turning the spanish mad' is the wordplay.
'turning' is a reversal indicator.
'the spanish' becomes 'el'.
'mad' becomes 'bats'.
'el'+'bats'='elbats'
'elbats' written backwards gives 'STABLE'.
(Other definitions for stable that I've seen before include "Place of birth" , "Well-balanced and steady" , "Horse establishment" , "Horse's house" , "'Firmly fixed, not moving (6)'" .)