熙 is a bound morpheme (b.f.) — it cannot stand alone as a word in modern Chinese. It appears in literary and formal compounds, often carrying connotations of brightness, prosperity, and harmony. You'll encounter it in fixed expressions like 熙熙攘攘 (bustling with activity) and 熙和 (warm and peaceful), as well as in the reign name 康熙 (Kāngxī). Its three core meanings — 'bright', 'prosperous', and 'merry' — are realized only within multi-character words or idioms.