Small piece of furniture is not wobbly (6)
I believe the answer is:
stable
'not wobbly' is the definition.
(I've seen this in another clue)
'small piece of furniture' is the wordplay.
'small' becomes 's' (abbreviation - e.g. clothes size).
'piece of furniture' becomes 'table' (table is a kind of piece of furniture).
's'+'table'='STABLE'
'is' acts as a link.
(Other definitions for stable that I've seen before include "Steady, constant" , "String may be kept in this" , "On an even keel" , "Animal accommodation is steady" , "Secure - fast - horses" .)