Staircase feature unfamiliar to the Spanish (5)
I believe the answer is:
newel
'staircase feature' is the definition.
(I've seen this in another clue)
'unfamiliar to the spanish' is the wordplay.
'unfamiliar' becomes 'new' (I've seen this in other clues).
'to the spanish' becomes 'el' ('the' in Spanish).
'new'+'el'='NEWEL'
(Other definitions for newel that I've seen before include "Main post supporting handrail on stairs" , "domestic post" , "Yucatan native" , "Post supporting stair rail" , "Post at the end of stairs" .)