In American terminology, an easy pace (6)
I believe the answer is:
canter
'pace' is the definition.
(cantering is a kind of pacing)
'in american terminology an easy' is the wordplay.
'in' indicates the answer is hidden within the clue.
'CANTER' is hidden in the letters of 'american terminology easy'.
(Other definitions for canter that I've seen before include "Gait between a trot and a gallop" , "Trance (anag) - horse's pace" , "Gallop easily" , "A slow easy gallop as for horse" , "Moderate pace for horse" .)