Hard to understand (9)
There are a few possibilities for this:
enigmatic
'hard to understand' is the definition.
(I've seen this in another clue)
This is all the clue.
(Other definitions for abstract that I've seen before include "Theoretical; abstruse" , "painting by Kandinsky, perhaps" , "Theoretical, not concrete" , "Kandinsky painting, for example?" , "sculpture by Hepworth" .)
'hard to understand' is the definition.
(I've seen this before)
This is all the clue.
(Other definitions for abstruse that I've seen before include "Obscure or recondite" , "Arcane" , "Incomprehensible to those with normal understanding" , "Difficult to comprehend" , "Strange busts are difficult to understand" .)
'hard to understand' is the definition.
(I've seen this before)
This is the entire clue.
(Other definitions for baffling that I've seen before include "Perplexing, bewildering" , "Mystifying" , "Mysterious" , "Hard to understand" , "Perplexing, puzzling" .)
(Other definitions for enigmatic that I've seen before include "Puzzling, like the Sphinx" , "Mystifying" , "Obscure, puzzling" , "Hard to fathom" , "Difficult to interpret" .)