偶然 (ǒu rán) is an adjective meaning 'accidental, by chance' — it describes events that happen without prior planning or intention. Unlike the adverb 偶尔 (ǒu ěr, 'occasionally'), which focuses on frequency, 偶然 emphasizes the lack of design; it is also broader than 巧合 (qiǎo hé, 'coincidental'), which specifically refers to two things happening together unexpectedly.