But the earliest occurrence is in a paper by Stuart Elden, in a discussion of Heidegger and Plato's Timaeus. Elden remarks: "There is something to be said for working with 'place' and 'placing', coining the neologism 'platial' to reflect its use in adjectival forms". This seems eminently sensible. And coincidentally (?) both writers figure heavily in my continuing research (of which this is only one gloss).