(literary) used to form a rhetorical question, similar to 岂 qǐ or "how could"

(literary) unexpectedly or to one's surprise; often used in the patterns 讵料 jù​liào or 讵知 jù​zhī to mean "who would have thought"

(literary) a marker used to express a condition, meaning "if" or "supposing"

(literary) ever; once (similar to 曾 céng)