WordWeb Online

1. Lacking clarity of meaning; causing confusion or perplexity
   "perplexing to someone who knew nothing about it"
   - confusing, puzzling

1. Be a mystery or bewildering to
   "a perplexing problem"
   - vex, stick, get, puzzle, mystify, baffle, beat, pose, bewilder, flummox, stupefy, nonplus, gravel, amaze, dumbfound
    
2. Make more complicated
   "There was a new development that perplexed the matter"
   - complicate

See also: muddy, unclear

Type of: alter, bedevil, befuddle, change, confound, confuse, discombobulate, fox, fuddle, modify, throw