Is it true that there is no uncle except a blood uncle, or is it permissible to address an elder as "O uncle"?

The questioner:
Is addressing the daughter of Hamzah evidence that an elder is honored by being called "O uncle" out of respect, as some people do?

The Shaykh:
No, he is a real uncle, because he is her uncle through breastfeeding. The Messenger of Allah (peace and blessings be upon him) was her uncle through breastfeeding. She said "O uncle," meaning through breastfeeding. As for people saying "O uncle" out of respect, or "O father," or "O brother," that is a good thing. These are good expressions out of respect and honor. Yes.

The questioner:
He also asks: Is it true that there is no uncle except a blood uncle?

The Shaykh:
Yes, indeed. This does not need a question. An uncle is only from blood or from breastfeeding, as mentioned before. As for an uncle in terms of respect and honor, that is a different matter; it is a matter of respect, not of blood or breastfeeding.