Synonyms of 'precursor'
1 forerunnerDictionary, pioneer, predecessorReal tennis, a precursor of the modern game, originated in the eleventh century.
2 heraldDictionary, usher, messengerThe deal should not be seen as a precursor to a merger.
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Your forebears are your ancestors.
I'll come back to the land of my forebears.
Something that is a harbinger of something else, especially something bad, is a sign that it is going to happen.
a harbinger of winter
Thesaurus for precursor from the Collins English Thesaurus
A precursor of something is a similar thing that happened or existed before it, often something which led to the existence or development of that thing.