'相似' (xiāngsì) is an adjective meaning 'similar' or 'resembling'—used to describe two or more things that share notable characteristics in appearance, behavior, structure, or function. The first character 相 (xiāng) conveys 'mutual' or 'each other', while 似 (sì) means 'to resemble' or 'to be like'. Together, they form a compound expressing mutual likeness—not identical, but closely alike in key ways. It’s commonly used in comparisons across domains like biology (e.g., species traits), design, language, or personal qualities.

This word typically follows the pattern 'A 和 B 相似' (A and B are similar) or appears after a noun with 的: '相似的特征' (similar features). It’s neutral in register—appropriate in both spoken and written Chinese—and often appears in academic, descriptive, or observational contexts. Unlike the verb 一样 (yíyàng, 'to be the same'), 相似 implies resemblance without claiming identity, making it precise for nuanced comparison.