The best replacement for costume is mask.

The best alternatives to costume are rated as following:
★★★★★  mask
★★★★  spiderman costume
★★★★  megatron costume
★★★★  attire
★★★  real jewelry
★★★  descize
★★★  disguise
★★  cosplay
★★  fancy dress
★  amazing spiderman costume
★  stormtrooper
★  outfit
★  set design
★  puppet

Your alternative for costume is not listed? Suggest!
Speaking about costume, one probably shouldn't forget about dressing up.

Other search terms related to costume and their ratings are:
★★★★★ dressing up
★★★★★ pink wig
★★★★ costume
You have in mind a companion for costume and it is not yet here? Propose!



Google Trends

Scale is based on the average worldwide traffic of costume in all years. Click on graph for more.
costume
mask
spiderman costume