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† ostrum, i, n.,  =  ὄστρεον. 
- I.  Lit., the blood of the sea-snail, purple (cf.: murex, purpura): ostro Perfusae vestes, Verg. A. 5, 111; Vitr. 7, 13.
 
- II.  Transf. 
 
- A.  Stuff dyed with purple, a purple dress, purple covering, purple: textilibus si in picturis ostroque rubenti Jacteris, Lucr. 2, 35: stratoque super discumbitur ostro, on purple-covered couches, Verg. A. 1, 700: Sarrano dormire ostro, id. G. 2, 506: velare umeros ostro, id. A. 7, 814; 4, 134; Prop. 4 (5), 3, 51: cenae sine aulaeis et ostro, Hor. C. 3, 29, 15; id. Ep. 1, 10, 26.
 
- B.  The brilliancy of purple, purple, Auct. Aetnae, 332.