Note: backward, dense and lacking courage (5)
I believe the answer is:
timid
'lacking courage' is the definition.
(I've seen this before)
'note backward dense' is the wordplay.
'note' becomes 'ti' (musical note, as in do re mi so fa la ti do).
'backward' is a reversal indicator.
'dense' becomes 'dim' (synonyms).
'dim' in reverse letter order is 'mid'.
'ti'+'mid'='TIMID'
'and' is the link.
(Other definitions for timid that I've seen before include "Bashful or fearful" , "Fearful - shy" , "afraid to speak out?" , "Easily frightened" , "Not assertive, retiring" .)