The German word for “surprise”, in the sense of an unexpected encounter, is “Überraschung” (f.). Its corresponding verb “to surprise” is “überraschen” and the adjective “surprised” is “überrascht”. Both the English and German words find their origin in the sense of a sudden attack (essentially “overtake”):

– “Ich war sehr überrascht als er ankam.” – “I was very surprised when he arrived.”
– “Ich freue mich auf die Überraschung.” – “I’m looking forward to the surprise.”
– “Wir verstecken uns um ihn zu überraschen.” – “We’re hiding in order to surprise him.”
– “Was für eine angenehme/unangenehme Überraschung.” – “What a pleasant/unpleasant surprise.”
– “Zu meiner großen Überraschung war alles weg.” – “To my great surprise everything was gone.”

Relatedly, “to take by surprise” (or “to overpower”) is “überrumpeln” in German:

– “Der Feind wurde total überrumpelt.” – “The enemy was totally taken by surprise.”