Horse stepped very softly out (5)
I believe the answer is:
steed
'horse' is the definition.
(I know that steed is a type of warhorse)
'stepped very softly out' is the wordplay.
'very softly' becomes 'pp' (abbreviation for pianissimo - very quietly).
'out' is a deletion indicator.
'stepped' with 'pp' taken out is 'STEED'.
(Other definitions for steed that I've seen before include "Warhorse" , "Trusty horse" , "Horse, mount" , "Literary term for horse" , "Stallion" .)