Definition of “frightening” - Learner’s Dictionary

frightening

adjective us uk /ˈfraɪtənɪŋ/
I found the story quite frightening.Starting school can be a frightening experience for children.A frightening number of people have got the disease.What's the most frightening thing that has happened to you?It's frightening to think that anyone could take a gun into a school.

B1 making you feel afraid or nervous:

a very frightening film
frighteningly adverb

(Definition of “frightening” from the Cambridge Learner's Dictionary © Cambridge University Press)