Scheme that is little short of perfect (4)
I believe the answer is:
idea
'scheme' is the definition.
(I've seen this in another clue)
'little short of perfect' is the wordplay.
'little' becomes 'l' (abbreviation for little).
'short of' indicates named letters should be taken away.
'perfect' becomes 'ideal' (similar in meaning).
'ideal' with 'l' taken out is 'IDEA'.
'that is' is the link.
(Other definitions for idea that I've seen before include "It comes to mind" , "Sudden inspiration?" , "Suggestion" , "a wheeze" , "Thought; concept" .)