The Chinese word 残留 is a compound formed by combining two meaningful characters: 残, which conveys notions of "remaining", "incomplete", or "damaged", and 留, which means "to stay", "to remain", or "to retain". When paired, the first character 残 modifies the second 留, creating a semantic unit where 残 emphasizes the incomplete or leftover nature of what remains. Thus, the compound 残留 means "to remain behind", "to be leftover", or "residue", specifically referring to something that persists, often undesirably, after the main part is gone, such as a chemical residue or a lingering trace. This formation follows the common Chinese morphological pattern of combining two semantically related characters to produce a new, more specific meaning.