Adam’s grandson once broke hearts (5)
I believe the answer is:
enoch
'adam's grandson' is the definition.
The definition suggests a singular noun which matches the answer.
'once broke hearts' is the wordplay.
'broke' is an anagram indicator.
'hearts' becomes 'h' (abbreviation used in card games e.g. bridge).
'once' anagrammed gives 'enoc'.
'enoc'+'h'='ENOCH'
Can you help me to learn more?
(Other definitions for enoch that I've seen before include "-- Powell, former politician" , "Name" , "Cain's eldest son - Methuselah's father" , "OT patriarch" , "greatly honoured" .)