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1. Become smaller or less in size, extent, or range
   "The amount of homework diminished towards the end of the semester";
   - decrease, lessen, fall
    
2. Lessen the authority, dignity, or reputation of
   "don't diminish your colleagues";
   - belittle

Derived forms: diminishes, diminishing, diminished

Type of: change magnitude, decrease, lessen, minify

Antonym: increase