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.

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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.
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Please tell me that different sentence structure.

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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.
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Thank you Mr. Micawber