Yesterday I was reading about the origins of various writing systems and when it got around to describing an alphabet some kind of background processing started in my head. In brief,
an alphabet is a set of letters used in a language (or more than one language). It had never occurred to me before but, just before it was explained in the text, I realised that the word was likely formed by the concatenation of two letters of the Greek alphabet, alpha (α) and beta (β).
This was not very surprising but odd that it had never occurred to me before. The definition of alphabet as a set of letters could reasonably interpreted as simply a collection of similar items in the same manner that we talk about a set of chairs or teeth. In this sense set does not imply any order.
The dictionary definitions and the one linked to at Wikipedia omit mention of sequence. Many (all?) alphabets, definitely the English alphabet, also define an order and the related word alphabetical. With the additional notion of order perhaps it is significant that the word alphabet is formed by the concatenation of the first and second letters of the Greek alphabet. I have found no confirmation of this thought anywhere!