Formerly vs. Formally

The cat dressed formally to attend the wedding. Formerly, he was in his pj's.

Formerly is an adverb. It means something that happened before. Previously.
Example: 
I had formerly been a teacher. Now I work in Strategic Communications.

Formally is also an adverb. It means something that is official. Officially.
Example:
I’m going to a wedding this Friday. My husband and I will both be formally dressed.  

​If it’s difficult to remember, just think of the root.
​Formerly = former
Formally = formal

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