A number that heartens listeners (3)
I believe the answer is:
ten
'a number' is the definition.
(ten is a number)
'heartens listeners' is the wordplay.
'TEN' is hidden in amongst the letters.
However, I am unsure how the hidden word is indicated.
'that' acts as a link.
Can you help me to learn more?
(Other definitions for ten that I've seen before include "time" , "Cardinal number" , "honour" , "PM's address, Downing St" , "Five times two" .)