Why called diffraction?

[Laurent Hodges <lhodges@IASTATE.EDU>]

> We shall try to
> maintain the convention that interference involves the deliberate
> production of two or more separate beams and that diffraction occurs
> naturally when a single wave is limited in some way.  We shall not always
> succeed in maintaining this convention because some names - the
> diffraction grating, for example - do not fit in with it and are too well
> established to change.

This is the distinction I've always made in class.  Then when discussing
the "diffraction grating" I point out that it should really be called an
"interference grating," and treat it as the N-slit interference pattern
where N is very large.  I hope this makes it clearer to students than just
calling it a "diffraction grating" with no comment.