Onwards or Since

Can we use the word " Onwards " in place of “since” where time is mentioned.

OR can we use “Since” in place of “Onwards”

I read this sentence in a dictionary

e.g. They lived there from the 1980s onwards.

can we use it as

They lived there since 1980s.

Does the both have sentences same meanings. please elaborate their difference.

In this case, the meanings are the same. I cannot guarantee that they are always synonymous, however, or that both can always be used-- note that they require different sentence structures.

Please tell me that different sentence structure.

You can see it yourself:

since the 1980ssince is a preposition.
from the 1980s onwardsonwards is an adverb

However, now that I consider it, onwards is irrelevant to the comparison: there is no relation in meaning between since and onwards. The adverb is an unnecessary addition, merely serving as emphasis: from the 1980s is sufficient, and is synonymous with since the 1980s.

Thank you Mr. Micawber