late 14c., "hinder, impede the movement of," originally by fastening a block of wood to something, from clog (n.). Meaning "choke up with extraneous matter" is 1670s; intransitive sense "become choked up with extraneous matter" is from 1755. Related: Clogged; clogging.
"fasten with or as if on a peg, drive pegs into for the purpose of fastening," 1590s, from peg (n.). Meaning "fix the market price" is by 1882. Slang sense of "identify, classify" is recorded by 1920. Related: Pegged; pegging.
"loop formed by fastening a running knot or slip-knot," mid-15c., perhaps from Old French nos or cognate Old Provençal nous "knot," from Latin nodus "knot" (from PIE root *ned- "to bind, tie"). Rare before c. 1600.
Meaning "that which holds two or more things firmly together" (on notion of clasping arms) is from mid-15c. Hence applied to various devices for fastening and tightening. Meaning "a prop, support," especially in architecture, is from 1520s. Of dogs, ducks, pistols, etc., "a couple, a pair" from c. 1400. Braces is from 1798 as "straps passing over the shoulders to hold up the trousers;" from 1945 as "wires for straightening the teeth."
"wedge-shaped piece or bolt which fits into a hole used in fastening or tightening," 1640s, of uncertain origin; perhaps a shortened form of cotterel, a dialectal word for "cotter pin or bolt, bracket to hang a pot over a fire" (1560s), itself of uncertain origin. Cotter-pin is attested by 1849.