Bicycle

Bicycle is the correct spelling.

If you become confused about the vowels, remember:

• The word cycle (which is always spelled this way) means a wheel, or something that can be diagrammed as a circle; and

• The prefix bi- (which always has the letter -i-) means 'two', or 'double'.

Etymological note: both elements come from the classical languages. "Bi-" is a Latin prefix. Κύκλος (kuklos), the original form of cycle, is a Greek word.