Grasp front of tartan rug (4)
I believe the answer is:
twig
'grasp' is the definition.
(twigging is a kind of grasping)
'front of tartan rug' is the wordplay.
'front of' indicates taking the first letters.
'rug' becomes 'wig' ('rug' is an informal term for a wig).
The initial letter of 'tartan' is 't'.
't'+'wig'='TWIG'
(Other definitions for twig that I've seen before include "Eventually grasp" , "Small tree shoot" , "Suddenly see; branchlet" , "Suddenly realise" , "Only a minor branch" .)