Expose more of text, namely by revolutionary movement (6)
I believe the answer is:
scroll
'expose more of text' is the definition.
(as in scrolling on a computer)
'namely by revolutionary movement' is the wordplay.
'namely' becomes 'sc' (abbrev for Latin scilicet meaning 'namely').
'by' says to put letters next to each other.
'revolutionary movement' becomes 'roll' (rolling or revolving round).
'sc'+'roll'='SCROLL'
(Other definitions for scroll that I've seen before include "Coiled parchment or paper" , "Move screen text around" , "Ancient book" , "Ancient text" , "Roll (of parchment. etc)" .)