Beginning of Egyptian sun god’s time (3)
I believe the answer is:
era
'time' is the definition.
(I know that era is a type of geologic time)
'beginning of egyptian sun god's' is the wordplay.
'beginning of' says to take the initial letters.
'sun god' becomes 'ra' (Egyptian god).
The initial letter of 'egyptian' is 'e'.
'e'+'ra'='ERA'
(Other definitions for era that I've seen before include "Significant time" , "Age of importance" , "Long historic period" , "Major division of geological time" , "US equality law" .)