希 is a bound form (b.f.) that primarily means 'hope' and almost always appears in the compound 希望 (xīwàng, 'hope'). It can also appear in less common words like 希冀 (xījì, 'aspire') or 希有 (xīyǒu, 'rare'). As a bound form, it cannot stand alone as an independent word — you must use it within a multi-character term.