Mark takes new heart from this narrow escape (5)
I believe the answer is:
scare
'this narrow escape' is the definition.
Although both the answer and definition are singular nouns, I can't see how one could define the other.
'mark takes new heart' is the wordplay.
'mark' becomes 'scar' (mark left by an injury).
'takes' means one lot of letters go next to another.
'heart' means to look at the middle letters.
The middle of 'new' is 'e'.
'scar'+'e'='SCARE'
'from' acts as a link.
Can you help me to learn more?
(Other definitions for scare that I've seen before include "Panic" , "Health worry" , "Greatly frighten" , "Frighten or intimidate" , "Startle" .)