Inflexible, as if in Fife (8)
I believe the answer is:
'inflexible' is the definition.
(similar in meaning)
I don't understand the remainder of the clue.
(Other definitions for ironclad that I've seen before include "Absolutely determined" , "Unassailable" , "Well armoured - perhaps an alibi?" , "monitor, for example" , "C 19 armoured warship" .)