Disown niece, oddly out of order (5)
I believe the answer is:
ionic
'order' is the definition.
(order of classical architecture)
'disown niece oddly' is the wordplay.
'oddly' indicates alternate letters (letters in the odd-numbered positions are used).
'disown'+'niece'='disownniece'
The alternating letters of 'disownniece' are 'IONIC'.
'out of' is the link.
(Other definitions for ionic that I've seen before include "Architectural order" , "Greek school" , "Support (a weight)" , "Old Greek" , "ancient order" .)