Fearful

wiktionary

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From Middle English ferful, fervol, equivalent to fear +‎ -ful.

etymonline

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fearful (adj.)

mid-14c., "causing fear," from fear (n.) + -ful. Meaning "full of fear, timid" (now less common) also is from mid-14c. As a mere emphatic, from 1630s. Related: Fearfully; fearfulness.