Proto-Indo-European root meaning "be sharp, rise (out) to a point, pierce."
It forms all or part of: acacia; acanthus; accipiter; acer; acerbic; acerbity; acervate; acervulus; acescent; acetic; acid; acicular; acme; acne; acrid; acridity; acrimony; acro-; acrobat; acromegaly; acronym; acrophobia; acropolis; acrostic; acrylic; acuity; aculeate; acumen; acupressure; acupuncture; acute; aglet; ague; Akron; anoxic; awn; coelacanth; dioxin; deoxy-; eager; ear (n.2) "grain part of corn;" edge (n.); egg (v.) "to goad on, incite;" eglantine; epoxy; ester; exacerbation; hammer; hypoxia; mediocre; oxalic; oxide; oxy-; oxygen; oxymoron; paragon; pyracanth; paroxysm; selvage; vinegar.
It is the hypothetical source of/evidence for its existence is provided by: Greek akros "at the end, at the top, outermost; consummate, excellent," akis "sharp point," akē "point of an iron tool," akantha "thorn," akmē "summit, edge," oxys "sharp, bitter;" Sanskrit acri- "corner, edge," acani- "point of an arrow," asrih "edge;" Oscan akrid (ablative singular) "sharply;" Latin acer (fem. acris) "sharp to the senses, pungent, bitter, eager, fierce," acutus "sharp, pointed," acuere "to sharpen," acerbus "harsh, bitter," acere "be sharp, be bitter," acus "a needle, pin," ocris "jagged mountain;" Lithuanian ašmuo "sharpness," akstis "sharp stick;" Old Lithuanian aštras, Lithuanian aštrus "sharp;" Old Church Slavonic ostru, Russian óstryj "sharp;" Old Irish er "high;" Welsh ochr "edge, corner, border;" Old Norse eggja "goad;" Old English ecg "sword;" German Eck "corner."
"to ring, jingle, give forth a sharp, metallic sound," early 14c., echoic (compare Dutch klinken, Old High German klingan, German klingen); perhaps a weakened form of clank. Transitive sense, "cause to produce a sharp metallic sound" is from late 14c. Related: Clinked; clinking.
"a sharp, hard, metallic sound," 1650s, from clank (v.). Reduplicated form clankety-clank attested from 1895.
"make a loud, sharp, resonant, metallic sounds," 1570s (intransitive), echoic (originally of trumpets and birds), akin to or from Latin clangere "resound, ring," and Greek klange "sharp sound," from PIE *klang-, nasalized form of root *kleg- "to cry, sound." Transitive sense is by 1850. Related: Clanged; clanging.
"to pierce with a sharp point of any kind," 1690s, from puncture (n.). Related: Punctured; puncturing.