An opening for many a relation (4,4,1,4)
I believe the answer is:
once upon a time
'an opening for many a relation' is the definition.
I know nothing about this answer so I cannot judge whether this works.
'an opening for many a relation' is the wordplay.
I cannot really see how this works, but
'an' could be 'i' (Roman numeral for one) and 'i' is located in the answer.
'many' could be 'm' (Roman numeral for a thousand) and 'm' is located in the answer.
'a' is present in the answer.
'relation' could be 'te' (te is a kind of relation) and 'te' is present in the leftover letters.
This explanation may well be incorrect...
Can you help me to learn more?
(Other definitions for once upon a time that I've seen before include "Start of a fairytale" , "Formerly" , "Long ago" , "Traditional start of a story" , "started any number of stories" .)