affirm

Concise Oxford English Dictionary © 2008 Oxford University Press:
affirm/əˈfɜːm/

▶verb state emphatically or publicly.

■ Law ratify (a judgement or agreement).

■ Law make a formal declaration rather than taking an oath.

– derivatives
affirmation noun,
affirmatory adjective,
affirmer noun.

– origin ME (in the sense ‘make firm’): via OFr. from L. affirmare, from ad- ‘to’ + firmus ‘strong’.