The compound word "撇下" is formed through the combination of the verb "撇" (piē), which means to cast aside, throw away, or neglect, and the directional complement "下" (xià), which indicates a downward movement or a resultant state of leaving something behind. Together, they create a phrasal verb where "下" modifies and completes the action of "撇," signifying the act of abandoning or leaving someone or something behind, often in a hurried or careless manner. This structure follows a common Chinese grammatical pattern where a verb is paired with a resultative complement to specify the outcome of the action, giving the term its specific meaning of desertion or forsaking.