Book penned by apprentice about revolution (5)
I believe the answer is:
orbit
'revolution' is the definition.
(orbit is a kind of revolution)
'book penned by apprentice about' is the wordplay.
'book' becomes 'b' (abbreviation for book).
'penned by' indicates putting letters inside.
'apprentice' becomes 'tiro' (I can't explain this - if you can you should believe this answer much more).
'about' says the letters should be written backwards.
'b' placed within 'tiro' is 'tibro'.
'tibro' reversed gives 'ORBIT'.
Can you help me to learn more?
(Other definitions for orbit that I've seen before include "Path of a planet or satellite" , "Rotating path" , "Circling path" , "Path of one celestial body around another" , "Moon's track" .)