1. number one; first; first place
俺が、一番じゃなきゃ気が済まない。I'm not satisfied unless I'm number one.
2. best; most
これが一番好きだよ。I like this one the best.
3. game; round; bout
4. as a test; as an experiment; by way of experiment; by way of trial; tentatively
5. song (e.g. in noh); piece