lit. proper behavior is based on reciprocity (idiom); fig. to return politeness for politeness
to come; (used as a substitute for a more specific verb); hither (directional complement for motion toward the speaker, as in 回来); ever since (as in 自古以来); for the past (amount of time); (prefix) the coming ...; the next ... (as in 来世); (between two verbs) in order to; (after a round number) approximately; (used after 得 to indicate possibility, as in 谈得来, or after 不 to indicate impossibility, as in 吃不来)