diminishing di·mi·nis·hing US/dɪˈmɪnɪʃɪŋ/ uncommon adjective 1. becoming smaller or less or appearing to do so “diminishing returns” “his diminishing respect for her” Similardecreasing WordNet 2.1 (Princeton University). CMU Pronouncing Dictionary. WordNet 2.1 Copyright Princeton University. All rights reserved.