Replaced Middle English ynde (late 13c., from Old French inde "indigo; blue, violet" (13c.), from Latin indicum). Earlier name in Mediterranean languages was annil, anil (see aniline). As "the color of indigo" from 1620s. As the name of the violet-blue color of the spectrum, 1704 (Newton).
1550s (n.), "native or inhabitant of Prussia;" 1560s (adj.), "of or pertaining to Prussia;" from Prussia + -an. In reference to the language of the earlier inhabitants of (East) Prussia, which was closely related to Lithuanian, by 1888. It was spoken between the lower Vistula and the Niemen and was extinct by the end of 17c. Prussian blue pigment (1724) came to English from French bleu de Prusse, so called for being discovered in Berlin, the Prussian capital.
All in all, it seems that Prussian blue was synthesised for the first time around 1706 by the Swiss immigrant Johann Jacob Diesbach in Berlin. [Jens Bartoll and Bärbel Jackisch, "Prussian Blue: A Chronology of the Early Years," in Zeitschrift für Kunsttechnologie und Konservierung 24, No. 1, 2010]
Early German sources refer to it as Preußisches Ultra-Marin and berliner blau. Prussic acid (1790), is from French acide prussique, so called in reference to Prussian blue pigment, to which it is chemically related.
Used in ancient Greece of a blue gem, perhaps sapphire, and of a purple or deep red flower, but exactly which one is unknown (gladiolus, iris, and larkspur have been suggested). It is fabled to have sprung from the blood of Hyakinthos, Laconian youth beloved by Apollo and accidentally slain by him. The flower is said to have the letters "AI" or "AIAI" (Greek cry of grief) on its petals. The modern use in reference to a particular flowering plant genus is from 1570s. Related: Hyacinthine.
Restricted sense of "drinking glass" is from early 13c. and now excludes other glass vessels. Meaning "a glass mirror" is from 14c. Meaning "glass filled with running sand to measure time" is from 1550s; meaning "observing instrument" is from 1610s.
fruit of the blackthorn, Old English slah (plural slan), from Proto-Germanic *slaikhwon (source also of Middle Dutch sleeu, Dutch slee, Old High German sleha, German Schlehe), from PIE *sleiə- "blue, bluish, blue-black" (see livid).
The vowel has been influenced by that in the old plural form, which according to OED persisted into the 17c. Scottish slae preserves the older vowel. Sloe-eyed is attested from 1804; sloe gin first recorded 1878.