Jelly, equally still (5)
I believe the answer is:
aspic
'jelly' is the definition.
(I know that aspic is a type of jelly)
'equally still' is the wordplay.
'equally' becomes 'as' (synonyms).
'still' becomes 'pic' (short for picture).
'as'+'pic'='ASPIC'
(Other definitions for aspic that I've seen before include "Stock set with food" , "Ending of Marlowe's thriller" , "Jelly based on fish or meat stock" , "Jelly made with fish or meat stock" , "Savoury jelly for coating meat, eggs etc" .)