Primary, initial (5)
I believe the answer is:
first
I believe this is a double definition.
'primary' is the first definition.
(associated in meaning)
'initial' is the second definition.
(similar in meaning)
(Other definitions for first that I've seen before include "Initial" , "& 2 Early new year arrivals bringing good luck" , "Method used in elections" , "best" , "Top university degree" .)