deadly

the word 'deadly' is a transparent compound from old english, formed by combining the adjective 'dead' with the suffix '-ly'. the old english root 'dēad' is of common germanic descent, related to dutch 'dood' and german 'tot', all conveying the state of having ceased to live. the suffix '-ly', from old english '-līc', originally meant 'body' or 'form', and was used to create adjectives meaning 'having the form or character of'. thus, 'deadly' literally means 'having the qualities of death', which evolved to describe something capable of causing death or, in extended use, something extremely potent or intense.

Structure: dead (lifeless) + ly (adjective/adverb suffix) dead (from old english 'dēad', of germanic origin, meaning lifeless); ly (from old english '-līc', a suffix forming adjectives meaning 'having the qualities of')