Can be at a corner untied... (5)
I believe the answer is:
loose
'untied' is the definition.
(synonyms)
'can be at a corner' is the wordplay.
'can' becomes 'loo' (loo is a kind of can).
'be at' means one lot of letters go next to another.
'a corner' becomes 'se' (the south east corner of something).
'loo'+'se'='LOOSE'
(Other definitions for loose that I've seen before include "Untie(d)" , "Relaxed; set free" , "Not firmly fixed" , "Grant freedom to" , "easy with one's favours" .)