I'm yet to move under small block (6)
I believe the answer is:
stymie
'block' is the definition.
('stymie' can be a synonym of 'block')
'i'm yet to move under small' is the wordplay.
'to move' is an anagram indicator.
'under' is a charade indicator (letters next to each other).
'small' becomes 's' (abbreviation - e.g. clothes size).
'im'+'yet'='imyet'
'imyet' with letters rearranged gives 'tymie'.
'tymie' put after 's' is 'STYMIE'.
(Other definitions for stymie that I've seen before include "Block or thwart, say a golf putt" , "Obstruction (originally at golf)" , "Hinder the progress of (something)" , "Old putting problem" , "balk" .)