Petite amie etymology in French

French word petite amie comes from French ami, and later French petit ami (Boyfriend (boy/man to whom one has a romantic attachment).)

Dictionary entry	Language	Definition
ami	French (fr)	Friend (one who is affectionately attached to another). Male friend.
petit ami	French (fr)	Boyfriend (boy/man to whom one has a romantic attachment).
petite amie	French (fr)	Girlfriend (girl/woman to whom one has a romantic attachment).

Petite amie etymology