* Unlike: "un-" is a prefix meaning "not" or "opposite of," and "-like" is a suffix meaning "having the characteristics of." So, "unlike" means "not like."
* Similarly: "similarly" is an adverb formed from the adjective "similar," which means "having a resemblance or likeness." The suffix "-ly" turns an adjective into an adverb.
Therefore, both words use a suffix (-like or -ly) to create a related word with a different grammatical function.