四周 has two distinct but related meanings, both derived from its characters: 四 (sì) means 'four', and 周 (zhōu) means 'week' or 'cycle/around'. As a noun, it most commonly means 'four weeks' — a standard unit of time roughly equivalent to one month. This usage appears in medical contexts (e.g., pregnancy timelines), project planning, and scheduling. As an adverb or noun meaning 'all around' or 'in all directions', it stems from the classical sense of 周 as 'perimeter' or 'circumference'; here, 四 emphasizes completeness in every direction (north, south, east, west). This spatial sense is literary or formal, often found in descriptive writing, poetry, or set phrases like 四周寂静 ('silence all around').

Although homophonous, the two senses are rarely ambiguous in context: time-related verbs or numbers nearby (e.g., 已经四周了, 过了四周) signal 'four weeks'; spatial verbs (e.g., 看四周, 四周都是...) or descriptive nouns (e.g., 四周的山) signal 'all around'. Native speakers distinguish them intuitively through syntax and collocation.