1. authority; expert; connoisseur; well-informed person
おお、その呼び方を知っているとはなかなかの通だな!Oh, you know it by that name? You're quite the connoisseur!
2. counter for messages, letters, notes, documents, etc.
メールが五通届いていた。Five emails had arrived.
3. understanding (esp. of male-female relations); tact; insight
4. supernatural powers; magical powers