主 is a bound morpheme (b.f.) in Chinese, meaning it cannot stand alone as an independent word but appears as the first or second element in many compounds. Its core senses include 'main' or 'primary' (主要, 主题), 'owner', 'master', or 'host' (主人, 车主), and 'Lord' or 'God' in religious contexts (主祷文, 主日). The religious sense is especially common in Christian terminology. As a bound form, its meaning is always determined by the compound it forms.