Undo ties I tangled very thoroughly (6-3)
I believe the answer is:
inside-out
'very thoroughly' is the definition.
(as in knowing something inside out)
'undo ties i tangled' is the wordplay.
'tangled' indicates an anagram.
'undo'+'ties'+'i'='undotiesi'
'undotiesi' anagrammed gives 'INSIDE-OUT'.
(Other definitions for inside-out that I've seen before include "US edition (anag.)" , "Thoroughly" .)