"white blood cell," regarded as an organism capable of devouring what it meets, 1884, from German phagocyten (plural), coined in German in 1884 by Dr. Elias Metchnikoff (1845-1916) from Greek phago- "eating, devouring" (from PIE root *bhag- "to share out, apportion; to get a share") + -cyte "cell." Related: Phagocytic.
word-forming element expressing state or condition, in medical terminology denoting "a state of disease," from Latin -osis and directly from Greek -osis, formed from the aorist of verbs ending in -o. It corresponds to Latin -atio.
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Harper, D. (n.d.). Etymology of phagocytosis. Online Etymology Dictionary. Retrieved $(datetime), from https://www.etymonline.com/word/phagocytosis