Upright, vertical (13)
I believe the answer is:
perpendicular
This clue is a double definition.
'upright' is the first definition.
(synonyms)
'vertical' is the second definition.
(I know that vertical can be written as perpendicular)
(Other definitions for perpendicular that I've seen before include "Style of late English Gothic church architecture" , "Like this answer [1A], relative to 1 dn" , "Sort of architecture" , "Gothic style following 7" , "At right angles" .)