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Almost certainly attributive use of the noun, though the noun sense we have is purportedly limited to chemistry. Other dictionaries have a noun. See Wiktionary:English adjectives. DCDuringTALK 21:00, 9 February 2011 (UTC)
I've added a 1794 citation. I put it in the adjective section (where it might belong if that section should exist), but it is doubtless also an attributive use. It is in the sense of the physics of music. — Pingkudimmi 01:39, 10 February 2011 (UTC)
I think my thinking on this kind of thing has been to rigidly synchronic. It would appear that the adjective came first and the noun followed. Thus, for some portion of the time this word was used in English, the adjective existed without the noun. That it does not appear in predicate position (often, ever?) or as a comparative or modified by "too" or "very" doesn't change that. Also, the noun and the adjective seem to differ a bit semantically. DCDuringTALK 02:05, 10 February 2011 (UTC)
Striking, tag removed: nominator seems to have changed his mind? —RuakhTALK 22:44, 1 July 2011 (UTC)