acrid: [18] Acrid is related to acid, and probably owes its second syllable entirely to that word. It is based essentially on Latin acer ‘sharp, pungent’, which, like acid, acute, oxygen, and edge, derives ultimately from an Indo-European base *ak- meaning ‘be pointed or sharp’. When this was imported into English in the 18th century, the ending -id was artificially grafted on to it, most likely from the semantically similar acid. => acid, acrylic, acute, edge, eglantine, oxygen, paragon
1712, formed irregularly from Latin acer (fem. acris) "sharp, pungent, bitter, eager, fierce," from PIE *akri- "sharp," from root *ak- "be sharp, rise (out) to a point, pierce" (cognates: Oscan akrid (ablative singular) "sharply;" Greek akis "sharp point," akros "at the farthest point, highest, outermost," akantha "thorn," akme "summit, edge;" also oxys "sharp, bitter;" Sanskrit acri- "corner, edge," acani- "point of an arrow," asrih "edge;" 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"). The -id suffix probably is in imitation of acid. Acrious (1670s) is a correct formation, but seldom seen.
