acanthus (n.)

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."

1550s, "medical extract of flowers," from French anthère or Modern Latin anthera "a medicine extracted from a flower," from Greek anthera, fem. of antheros "flowery, blooming," from anthos "flower," from PIE root *andh- "to bloom" (source also of Sanskrit andhas "herb," Armenian and "field," Middle Irish ainder "young girl," Welsh anner "young cow"). The botanical sense of "polliniferous part of a stamen" attested by 1791.

in zoology, "having a spiny head," 1847, from acantho- (see acanthus) + Latinized adjectival form of Greek kephalē "head" (see cephalo-) + -ous.