deleterious

Etymology

Borrowed (1640s, 1582 as deletorious) from Medieval Latin deleterius, deletorius, from Ancient Greek δηλητήριος (dēlētḗrios, “noxious, deleterious”), from δηλητήρ (dēlētḗr, “a destroyer”), from δηλέομαι (dēléomai, “I hurt, damage, spoil, waste”).

adj

1. Harmful, often in a subtle or unexpected way.
   deleterious effects
   deleterious to someone's health
   Or might it suffice him, that every wholesome growth should be converted into something deleterious and malignant at his touch? 1850, Nathaniel Hawthorne, “chapter XV”, in The Scarlet Letter
   A trolleybus service was established by the London Passenger Transport Board between North Woolwich and Stratford on February 6, 1938, and had a deleterious effect on railway passenger traffic. 1946 May and June, J. G. Holmes, “The North Woolwich Branch”, in Railway Magazine, page 176
   The advent of the smartphone and its cousin the tablet was followed quickly by hand-wringing about the deleterious effects of “screen time.” But the impact of these devices has not been fully appreciated, and goes far beyond the usual concerns about curtailed attention spans. 2017 September, Jean M. Twenge, “Have Smartphones Destroyed a Generation?”, in The Atlantic
2. (genetics) Having lower fitness.