blade (n.) Look up blade at Dictionary.com
Old English blæd "a leaf," but also "a leaf-like part" (of spade, oar, etc.), from Proto-Germanic *bladaz (cognates: Old Frisian bled "leaf," German blatt, Old Saxon, Danish, Dutch blad, Old Norse blað), from PIE *bhle-to-, suffixed form (past participle) of *bhel- (3) "to thrive, bloom," possibly identical with *bhel- (2) "to blow, swell" (see bole). Extended in Middle English to shoulders (c.1300) and swords (early 14c.). The modern use in reference to grass may be a Middle English revival, by influence of Old French bled "corn, wheat" (11c., perhaps from Germanic). The cognate in German, Blatt, is the general word for "leaf;" Laub is used collectively as "foliage." Old Norse blað was used of herbs and plants, lauf in reference to trees. This might have been the original distinction in Old English, too. Of men from 1590s; in later use often a reference to 18c. gallants, but the original exact sense, and thus signification, is uncertain.