Assertor

as·sert  (-sûrt)

tr.v. as·sert·ed, as·sert·ing, as·serts

1. To state or express positively; affirm: asserted his innocence.

2. To defend or maintain (one's rights, for example).

Idiom:

assert oneself

To act boldly or forcefully, especially in defending one's rights or stating an opinion.

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[Latin asserere, assert- : ad-, ad- + serere, to join; see ser-² in Indo-European roots.]

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as·serta·ble, as·serti·ble adj.

as·serter, as·sertor n.