deleterious
del-ih-TEER-ee-usadjMeaning harmful, often in a way that is not obvious at first
Memory hook DELETE-erious: it DELETES the good. A sneaky computer bug deletes one of Sami’s files every night, until his whole science project is nearly gone; the bug is deleterious.
Too much sun can have deleterious effects on your skin.
In context The chemical seemed safe in short tests, but over the years it proved deleterious, slowly weakening the shells of the birds whose food it touched.
Similar harmful, damaging, injurious, destructive
Opposite beneficial, salutary, wholesome
From Greek deleterios, “harmful,” from deleisthai (to hurt).