The following should work. The lambda function filter out the duplicated words.
inputs=[]
input = raw_input("Word: ").strip()
while input:
inputs.append(input)
input = raw_input("Word: ").strip()
uniques=reduce(lambda x,y: ((y in x) and x) or x+[y], inputs, [])
print 'There are', len(uniques), 'unique words'