This is the 682nd most frequent Czech word.
nečekaně
Unexpectedly.
In this sentence, 'nečekaně' is used as an adverb to describe an action (starting to rain) that happened without prior expectation or prediction.
Nečekaně začalo pršet.
Unexpectedly, it started raining.
Here, 'nečekaně' is used as an adverb to describe an unexpected quality (sincerity) of something (the answer).
Jeho odpověď na otázku byla nečekaně upřímná.
His answer to the question was unexpectedly sincere.
In this instance, 'nečekaně' serves as an adverb emphasizing the unforeseen nature of the event (meeting on the street).