1 shock, astound, astonish, amaze, disconcert, nonplus, dumbfound or dumfound, stagger, take aback, strike, hit, Colloq floor, bowl over, flabbergast, rock or set (someone) back on his or her or Chiefly Brit their heels, Brit knock (someone) for six, US knock (someone) for a loop:
What surprised me was her coolness in the face of danger.
2 take or catch unawares, catch red-handed or in the act or in flagrante delicto, catch napping or off guard, discover:
When Samuel Johnson's wife found him with a maid, she said, 'Dr Johnson! I am surprised!', to which he replied, 'No, madam: you are amazed. I am surprised.'
3 shock, astonishment, amazement, stupefaction, wonder, incredulity:
Imagine my surprise to learn that I was being arrested.
4 blow, jolt, shocker, bolt from or US also out of the blue, bombshell, eye-opener:
It came as a surprise to me that my sister was pregnant.