verb
affirm
uh-FURM/əˈfɜːrm/
To state firmly that something is true, valid, or worthy of support.
The witness appears ready to affirm the statement firmly.

Etymology
The image of making something firm developed into confirming or corroborating it. To affirm a statement is to give it that figurative firmness by declaring it true.
In context
when he tried to be a notary he was denied because he refused to affirm a belief in the Supreme Being
More examples
- The court affirmed the earlier decision.
- He publicly affirmed his support for the proposal.
- The ceremony affirms their commitment to one another.
Forms
affirm · affirms · affirmed · affirming
affirmation noun — a firm declaration or expression of support