OK... Now I just need to figure out what term I'd mentally transposed with the term "pentatonic". Probably harmonic-something-or-other...? I was thinking of the natural scale of (valveless) brass instruments, which presumably was the medium via which Mozart accidentally spawned a bawdy marching song: G, C, E, G, sort-of-Bb-ish, and C-if-you-can-blow-hard-enough - which is 6 notes, of course, but there's a blues style of composition that, despite not having the restrictions of the humble brass tube, teases the Bb a lot and deliberately avoids ever rising to the C, except possibly on the very last note. I suspect I've heard that style erroneously referred to as "pentatonic" at some point and absorbed the muddlification.

I'm burbling, gimme sleep... [SNORE] =:o}