An adverb meaning 'extremely' or 'severely', used to intensify a negative condition or strong feeling (adverbial form of ひどい).
彼の怪我はひどく腫れている。
His injury is terribly swollen.
試験の結果にひどく落ち込んだ。
I was terribly disappointed by the exam results.
天候がひどく悪く、試合は中止になった。
The weather was so bad the match was canceled.
その事件は世間でひどく批判された。
That incident was severely criticized by the public.