copula/ˈkɔpjulə; `kɑpjələ/ n(grammar) type of verb that connects a subject with its complement 系词（即连系动词, 用以连结主语及其补语） In `George became ill', the verb `became' is a copula. 在Georgebecameill一句中, became是系词.
牛津英汉双解词典