Hiya, insel! "Purify by fire" is what came into my head when I read your subect title. (Aside: get a load of this quote from today's Word: Friedrich Bayer and Friedrich Weskott were two buddies who set up an international paint and dye company in Germany in 1863. Scientists in 1886 discovered an antipyretic painkiller could be manufactured from the waste of one of the dye products. So, in 1888, the pair set up a pharmaceutical department." I never knew that aspirin was developed from waste, esp. from waste that was likely to be poisonous.) Anyway, except for saying Middle English, Gurunet agrees with your source:
pure (pyʊr)
adj., pur·er, pur·est.

1. Having a homogeneous or uniform composition; not mixed: pure oxygen.
2. Free from adulterants or impurities: pure chocolate.
3. Free of dirt, defilement, or pollution: “A memory without blot or contamination must be . . . an inexhaustible source of pure refreshment” (Charlotte Brontë).
4. Free of foreign elements.
5. Containing nothing inappropriate or extraneous: a pure literary style.
6. Complete; utter: pure folly.
7. Having no faults; sinless: “I felt pure and sweet as a new baby” (Sylvia Plath).
8. Chaste; virgin.
9. Of unmixed blood or ancestry.
10. Genetics. Produced by self-fertilization or continual inbreeding; homozygous: a pure line.
11. Music. Free from discordant qualities: pure tones.
12. Linguistics. Articulated with a single unchanging speech sound; monophthongal: a pure vowel.
13. Theoretical: pure science.
14. Philosophy. Free of empirical elements: pure reason.
[Middle English pur, from Old French, from Latin pūrus.]

pure'ly adv.
pure'ness n.
SYNONYMS pure, absolute, sheer, simple, unadulterated. These adjectives mean free of extraneous elements: pure gold; absolute oxygen; sheer alcohol; a simple substance; unadulterated coffee.