偕 is a literary bound form (b.f.) meaning 'in the company of' or 'together with'. It cannot stand alone and appears in formal compounds such as 偕同 (xié tóng, 'together with'), 偕老 (xié lǎo, 'to grow old together'), and 偕行 (xié xíng, 'to travel together'). You'll encounter it in written Chinese, classical texts, and formal speeches, not in everyday conversation.