Collar head of Yard easily remembered? (6)
I believe the answer is:
catchy
'easily remembered?' is the definition.
(I've seen this before)
'collar head of yard' is the wordplay.
'collar' becomes 'catch' ('catch' can be a synonym of 'collar').
'head of' says to take the initial letters.
The first letter of 'yard' is 'y'.
'catch'+'y'='CATCHY'
(Other definitions for catchy that I've seen before include "Of tune, pleasant and easily remembered" , "Hummable" , "(Of tune) infectious" , "Type of tune that stays in the memory" , "Staying in the mind of a tune" .)