spoonerism

n. A slip of the tongue in which two sounds are unintentionally transposed in a way to give a different meaning to the utterance, which is sometimes humorous as in saying “The weight of rages will press hard upon the employer” instead of “The rate of wages will press hard upon the employer.” Or in saying “A well-boiled icicle is a joy to ride” instead of “A well-oiled bicycle is a joy to ride.”