This is the 524th most frequent Croatian word.
jesu
"Jesu" is the Croatian plural form of the verb "to be," meaning "are."
In this sentence, 'Jesu' is used as part of a question to ask whether something happened or a state is true. It is the auxiliary verb representing 'are they' in the present tense third person plural question form.
Jesu li oni uopće stignuli na vrijeme?
Did they even arrive on time?
'Jesu' here acts as the auxiliary verb in a hypothetical conditional clause to confirm a presumption or state. It represents 'they did' or 'they are' depending on the contextual implication in this subordinate clause.
Ako jesu, trebali bismo ih dočekati.
If they did, we should greet them.
In this usage, 'Jesu' is used for emphasis, affirming the statement about the subject 'they.' It expresses certainty and emphasis, similar to adding 'indeed' or 'certainly' in English statements.