function word
noun [ C ] language specialized uk/ˈfʌŋk.ʃən ˌwɜːd/ us/ˈfʌŋk.ʃən ˌwɝːd/
功能词（语法里，像连词、前缀词或代名词等词语，用在句子或词组中表示其他词语间的关系）
in grammar, a word such as a conjunction, preposition, or pronoun that is used to show the relationship between other words in a sentence or phrase