'偶然' (ǒu rán) literally combines 偶 (ǒu), meaning 'occasional' or 'by chance', and 然 (rán), a classical suffix indicating manner or state — together forming an adverb meaning 'by chance' or 'accidentally'. Unlike the verb '碰巧' (pèng qiǎo), which emphasizes fortunate coincidence, 偶然 stresses the unplanned, random nature of an event — often with neutral or slightly formal tone. It commonly modifies verbs (e.g., 遇见, 发现, 听到) and appears in written and spoken Chinese alike, especially when describing unexpected encounters, discoveries, or outcomes.

This word is frequently used in narratives, news reports, and everyday explanations to clarify that something was not intentional or premeditated. While it can appear as a noun in rare literary contexts (e.g., '这是个偶然'), its overwhelming usage is adverbial. Learners should note that it cannot directly modify nouns without additional structure (e.g., 偶然的事件 requires 的), unlike English 'accidental', which functions both adjectivally and adverbially.