Deference about Old Right, revolutionary in hindsight (10)
I believe the answer is:
retrospect
'hindsight' is the definition.
(I've seen this before)
'deference about old right revolutionary' is the wordplay.
'deference' becomes 'respect' ('respect' can be a synonym of 'deference'**).
'about' indicates putting letters inside.
'old' becomes 'o' (common abbreviation eg in OE for Old English).
'right' becomes 'rt'.
'revolutionary' says the letters should be written in reverse.
'o'+'rt'='ort'
'ort' back-to-front is 'tro'.
'respect' placed around 'tro' is 'RETROSPECT'.
'in' is the link.
(Other definitions for retrospect that I've seen before include "Survey of past events" , "Contemplation of the past" , "Look(ing) back" , "A backward view" , "Hindsight" .)