This is the 8473rd most frequent French word.
affirmatif
Affirmative; expressing agreement or consent.
Here, 'affirmative' describes a type of response, indicating agreement or confirmation.
Sa réponse était affirmative.
His response was affirmative.
In this context, 'affirmative' is used adjectivally to describe the nod as confirming or agreeing.
Il a donné un signe affirmatif de la tête.
He gave an affirmative nod.
Here, 'affirmatif' metaphorically describes the speaker's attitude or state of mind as being positive or affirming.