frighten
verb
make (someone) afraid or anxious.
the savagery of his thoughts frightened him
scare,startle,alarm,terrify,petrify,shock,chill,appal,agitate,panic,throw into panic,fluster,ruffle,shake,disturb,disconcert,unnerve,unman,intimidate,terrorize,cow,daunt,dismay,fill someone with fear,strike terror into,put the fear of God into,chill someone’s blood,chill someone to the bone,chill someone to the marrow,make someone’s blood run cold,freeze someone’s blood,make someone’s flesh crawl,give someone goose pimples,scare stiff,scare witless,scare someone (half) to death,scare the pants off,rattle,spook,throw into a blue funk,put the wind up,make someone’s hair curl,scare the bejesus out of,affright,terrifying,horrifying,alarming,startling,shocking,chilling,spine-chilling,hair-raising,blood-curdling,appalling,disturbing,disconcerting,unnerving,intimidating,daunting,dismaying,upsetting,harrowing,traumatic,eerie,sinister,fearsome,dreadful,horrible,awful,nightmarish,monstrous,grim,gruesome,macabre,menacing,eldritch,scary,spooky,creepy,hairy,scare shitless