A long seat, but so far short (4)
I believe the answer is:
sofa
'a long seat' is the definition.
(I've seen this before)
'so far short' is the wordplay.
'short' means to remove the last letter.
'far' with its last letter taken off is 'fa'.
'so'+'fa'='SOFA'
'but' is the link.
(Other definitions for sofa that I've seen before include "Upholstered seating" , "Upholstered seat for more than one person" , "Upholstered seat for two or more" , "Comfy piece of furniture" , "Living room seat" .)