Quotation from www.quora.com
The abbreviation “no.” for the word “number” comes from the numero symbol, № (also written as “No.” or “no.”), which is in turn derived from Latin numero. As you can see, it has an “o” in it.
Then do you know by the way, what the abbreviations of e.g., i.e., etc., are derived from?
i.e. is abbreviation of Latin expression of id est, which means “that is” in Latin. It introduces a rewording or a clarification of a statement.
e.g. is abbreviation of exempli gratia in Latin, which means “for example” or “for instance”. It introduces one or more examples that illustrate something stated.
etc. is abbreviation of et cetera in Latin phrase, which introduces a number of unspecified additional items (persons or things).