That which defragments; a program that performs defragmentation.(noun)
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Use "defragmenter" in a sentence
"Continuing with the analogy of the file cabinet, a defragmenter is the helpful assistant that comes in and alphabetises all your documents in the appropriate folders and file drawers for you."
"Notice the defragmenter is the last of what should be checked for open iDefrag and check to see if the drive is heavily fragmented (shown in the "Statistics" section)."
"Continuing with the analogy of the file cabinet, a defragmenter is the helpful assistant that comes in and alphabetizes all your documents in the appropriate folders and file drawers for you."