WordWeb Online

1. A mistake that results from taking one thing to be another
   "he changed his name in order to avoid mix-up with the notorious outlaw";
   - confusion

1. Assemble without order or sense
   "She mixes up the words when she is supposed to write a sentence";
   - jumble, confuse
    
2. Cause to be perplexed or confounded
   - stump

Derived forms: mix-ups, mixed up, mixing up, mixes up

See also: conflate

Type of: assemble, baffle, beat, bedevil, befuddle, bewilder, confound, confuse, discombobulate [informal], dumbfound, error, fault, flummox, fox, fuddle, get, gravel, mistake, mystify, nonplus, perplex, piece, pose, put together, puzzle, set up, stick, stupefy, tack, tack together, throw, vex