Most of the optics texts which I have used acknowledge this semantic
confusion and include a statement something like this example (from Lipson
et al,Optical Physics, 3rd ed, pg 152):
" . . . There is another class of phenomena that is closely related to
diffraction, These are produced by the superposition of several spatially
distinguishable waves and are called "interference" phenomena. Diffraction
and interference are sometimes not easily distinguishable, and different
writers attach different meanings to the two words. 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. But we shall try to preserve the distinction
wherever we can. It is, in fact, similar to the distinction between the
Fourier series (corresponding to interference) and the Fourier transform
(diffraction); it will be remembered that the series can be deduced as a
special case of the transform, and in the same way all interference can be
explained on the basis as diffraction effects."
A looser analogy reminds me of the semantic hassles over "heat" vs "work"
in applying the first law of thermo.