是情态动词，完整形式是modal verb，例如：

1.The modal verb hui has two basic meanings: ability and possibility.情态动词会有两个基本意义：能力与可能。

2.A Model of Word Sense Disambiguation of English Modal Verb May by a Neural Network.基于人工神经网络构建英语情态动词may的语义排歧模型。