Part of speech: Adjective
extreme in degree or extent or amount or impact
Example: in a frightful hurry; spent a frightful amount of money
, Fearful, Awful, Tremendous, Frightful
The word "frightful" comes from Old English forhtful, which comes from Middle English frightful.
fright – A related word in the same word family.
ful – A related word in the same word family.
Old English was a fully Germanic language before the Norman Conquest transformed it.