> you can actually find this used quite a bit in discussions of stress and syllabication/syllabification.

scene - interior, consultant's room, view of LA thro' window
Consultant: So, tell me, what triggers this overwhelming stress?
Patient: It’s the syllables, doctor – every time I see antepenultimate I get in a tizzy because I don’t know if they mean fourth from last or third from last!

but here's my question: preantepenultimate is often defined as 'fourth from last'; why isn't it third from the last?

tsory, didn't mean to ignore your question. We might some of us remember this cropping up from Anu a while ago.

It seems to me rather a confusion about what the label means – in other words, “third to last” may sound like it should be three behind the last, but the expression has grown up evidently meaning otherwise: ‘second to last’ commonly is clear as ‘the horse that came in ahead of only one other’ – it was (in this topsy-turvy inverted frame of reference) placed second, surpassed by only one in the race to the bottom.
Hm, that’s prolly as clear as mud but.