It begins though it must end - eventually? (4)
I believe the answer is:
time
This clue might be a double definition.
'it begins though it must end' is the first definition.
The definition suggests a singular noun which matches the answer.
'eventually?' is the second definition.
(thesaurus)
Can you help me to learn more?
(Other definitions for time that I've seen before include "See 12" , "Speech to close pub" , "The fourth dimension?" , "Prison sentence; occasion" , "It's measured by watch or clock" .)