devaient

/dəvɛ/devoir
1.
verbIndicative3rdImperfectPlural3

had to

were supposed to

Ils devaient partir à huit heures, mais le train avait du retard.

They were supposed to leave at eight, but the train was late.

2.
verbIndicative3rdImperfectPlural3

must have been

were probably / were likely to be

À en juger par leur visage, ils devaient être épuisés.

Judging by their faces, they must have been exhausted.