(of) a statement expressing 'Yes', agreement etc or one that is true, real etc as in 'The answer is (in the) affirmative
being agreeable or assenting
Cases of word usage
1) (of) a statement expressing 'Yes', agreement etc or one that is true, real etc as in 'The answer is (in the) affirmative (affirmative)
2) an expression of a positive feeling or affirmative statement by using a negative one, as in 'I shall not be sorry when it's over' (litotes)