孤 is a bound form (b.f.) that cannot stand alone; it appears in compounds meaning 'solitary', 'isolated', or 'orphaned'. It also has a historical self-reference use: emperors and princes would call themselves 孤 (I, my) to denote their unique and lonely position. In modern Chinese, it most commonly occurs in words like 孤独 (lonely), 孤立 (isolated), and 孤儿 (orphan).