Suddenly, it started to hail, and we had to take cover.

hail 是名词，指"冰雹"，即从云层中降落的固态降水颗粒，通常呈球形或不规则形状。作为动词时表示"下冰雹"。 take cover 是固定短语，cover 指"遮蔽物、掩护"，take cover 字面意思是"取得掩护"，引申为"躲避、找掩护"的意思。