Force into action (5)
'force into action' is the definition.
(I've seen this in another clue)
This is the entire clue.
(Other definitions for impel that I've seen before include "Urge forward, drive" , "Urge or propel" , "Urge or force to action" , "Oblige" , "Make" .)
(Other definitions for compel that I've seen before include "'Force, oblige (6)'" , "drive on" , "Make someone do something" , "Urge on, force" , "Force, oblige to do something" .)