This is the 216th most frequent Icelandic word.
höfðu
"Had" (past tense of "have").
In this sentence, 'höfðu' is used as the imperative form of the verb 'að hafa', instructing one or more people to 'have' or 'enjoy' something.
Höfðu gaman af tónlistinni.
Enjoy the music.
Here, 'höfðu' is used as the third-person plural past indicative form of 'að hafa', denoting past perfect tense.
Þau höfðu aldrei séð slíkan storm.
They had never seen such a storm.
In this interrogative sentence, 'höfðu' functions as the second-person plural past indicative form of 'að hafa', asking about something in the past.