An aglet keeps the fibers of the lace or cord from unraveling, plus its firmness and narrow profile makes it both easier to hold and easier to feed through the eyelets, lugs or other lacing guides.
Picken, Mary Brooks: The Fashion Dictionary , Funk and Wagnalls, 1957. (1973 edition ISBN 0308100522) This in turn comes from "acus", the original Latin word for needle. An aglet is thus like a small "needle" at the end of a cord.
Many were highly ornamental, and made of precious metals such as silver. Before the invention of buttons, they were used on the ends of ribbons to fasten clothing together. Sometimes they would be formed into small figures. Shakespeare calls this type of figure an "aglet baby" in The Taming of the Shrew.
Source: Wikipedia > Aglet
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