bad cold
A common phrase for a severe cold, often used when symptoms are strong or prolonged.
I caught a bad cold and was bedridden for a whole week.
He has a bad cold and can't speak.
Standard kanji-kana mixed spelling.
Kanji spelling for ひどい; less common in everyday writing but seen in literary or formal contexts.
Compound of ひどい (severe) and 風邪 (cold). The phrase is transparent and follows standard adjective-noun modification.