Nothing other than; perpendicular (5)
I believe the answer is:
sheer
This clue is a double definition.
'nothing other than' is the first definition.
(I've seen this before)
'perpendicular' is the second definition.
(synonyms)
(Other definitions for sheer that I've seen before include "Gossamer or precipitous" , "Downright - deviation" , "Absolutely - diaphanous" , "Unmitigated; perpendicular" , "Very thin and fine" .)