This is the 13686th most frequent Russian word.
неожиданным
Unexpected.
The word 'неожиданным' describes the surprising nature of the event (a feminine noun 'приезд').
Ее приезд был неожиданным.
Her arrival was unexpected.
Here, 'неожиданным' relates to the noun 'событие', indicating it was surprising and not anticipated.
Это событие оказалось неожиданным для всех.
This event turned out to be unexpected for everyone.
In this case, 'неожиданное' modifies the noun 'решение', specifying that the decision was surprising and unanticipated.