Deer by the sound of it showing courage (5)
I believe the answer is:
heart
'courage' is the definition.
(heart is a kind of courage)
'deer by the sound of it' is the wordplay.
'deer' becomes 'hart' (hart is a kind of deer).
'by the sound of it' indicates a 'sounds like' (homophone) clue.
'hart' sounds like 'HEART'.
'showing' acts as a link.
(Other definitions for heart that I've seen before include "Feeling" , "Body organ" , "Vital part" , "Muscular organ for blood circulation" , "Playing card - pity" .)