IPA: /prɪˈmɛrɪtəli/
KK: /prɪˈmɛrɪtəli/
In a manner that occurs before a marriage takes place.
They decided to live together premaritally to see if they were compatible.
Premaritally → It is formed from "pre-" (meaning before) and "maritalis" (from Latin "maritus", meaning married). The word refers to the time or state before marriage.
Think of 'pre-' meaning before and 'maritalis' relating to marriage — so premaritally refers to the time before one is married.