Why is "lens" singular and "lenses" plural? Why isn't "lens" the plural of "len"?

@SW-User Yes...same as with bus and buses.

@Callmyname no coz words are not created whimsically. There's a scientific pattern through which most words are created or derived. This includes pronunciation.

@Callmyname words which are included in dictionary and used in academic purposes are never created whimsically. Instead of giving false arguments you should update yourself how linguistics works. Also, majority of the English words are borrowed from other languages. Even the letter 'I' is derived from germanic 'ich'. And you from 'euch'. Now a lot people say 'you' as 'ya' but 'ya' has no value in linguistics.