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1620s, from Latin parasiticus, from Greek parasitikos "of or pertaining to a parasite; the trade of a parasite," from parasitos (see parasite). Biological sense is from 1731. Related: Parasitical, 1570s in reference to toadies; from 1640s in the biological sense.
parasitic par·a·sit·ic (pār'ə-sĭt'ĭk) or par·a·sit·i·cal (-ĭ-kəl)
Of, relating to, or characteristic of a parasite.
Caused by a parasite.