Breakdown of Bienvenue !
Questions & Answers about Bienvenue !
Bienvenue is the feminine singular form of the adjective bienvenu / bienvenue.
In the one-word exclamation Bienvenue !, French traditionally uses the feminine form because it comes from an older expression understood like Je vous souhaite la bienvenue or Soyez la bienvenue / Soyez le bienvenu, depending on context. Over time, Bienvenue ! became a fixed greeting, and the spelling with -e is the standard form when used by itself on signs, in greetings, and in everyday use.
So even if you are welcoming a man, a woman, or a group, the standalone greeting is usually just Bienvenue !
Not really in the strict grammatical sense. It is more like a fixed expression or elliptical phrase.
French often leaves out words that are understood from context. So Bienvenue ! works like a full greeting even though it does not include a verb.
You can think of it as a shortened form of something like:
But in real life, Bienvenue ! stands perfectly well on its own.