This is the 115th most frequent Polish word.
mieli
"Mieli" means "they had" or "they were having" (past tense of "mieć" – to have).
Used as the past tense form of the verb 'mieć' (to have) for the third person plural.
Oni mieli dużo pracy wczoraj.
They had a lot of work yesterday.
Here 'mieliście' is used, which is the second person plural past tense form of 'mieć'.
Czy mieliście już okazję odwiedzić to miejsce?
Have you already had the chance to visit this place?
Again, past tense of 'mieć' but used to refer to general possession in the past.