Denshi Jisho — Online Japanese dictionary

脅かす おどかす 1: to threaten; to menace;
2: to startle; to surprise
Common word, Godan verb with su ending, Transitive verb 
脅かす おびやかす 1: to intimidate; to scare;
2: to jeopardize; to endanger; to imperil
Common word, Godan verb with su ending, Transitive verb 

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