Other forms: decluttering; decluttered; declutters
To declutter is to tidy up a mess, especially by getting rid of objects. You might declutter your bedroom by donating your old clothes and recycling those magazines you never read.
Clutter was originally a verb, used in the 1500s to mean "collect in heaps" or "form clots." Declutter is a much younger word, dating from the mid-20th century. When you clean and organize a space, removing extra stuff that you really don't need, you declutter. This can mean pulling out all your sweaters and giving the ones you never wear to your younger sibling, or disassembling your collection of cat memorabilia and only keeping your three favorite objects.