The word "回国" is a verb-object compound formed by combining the verb "回" (huí), meaning "to return" or "to go back," with the noun "国" (guó), meaning "country." In this construction, the action of returning is directed toward the object, one's homeland, so the literal sense is "to return to [one's] country." It functions as a single lexical unit meaning "to return to one's home country" from abroad.