Knot in lace - it's stiff (9)
'stiff' is the definition.
(I've seen this before)
'knot in lace it's' is the wordplay.
'knot' indicates anagramming the letters (I've seen 'knotted' mean this).
'inlaceits' is an anagram of 'INELASTIC'.
(Other definitions for inelastic that I've seen before include "Rigid", "unable to bend?", "Non-stretch", "Broken", "stiff".)