accretionEnglishOxford American Thesaurusaccretion noun 1 the accretion of sediments in coastal mangroves: accumulation, collecting, gathering, amassing, cumulation, accrual, growth, formation, enlargement, increase, gain, augmentation, rise, mushrooming, snowballing; rare amassment. 2 the city has a historic core surrounded by recent accretions: addition, extension, growth, appendage, add-on, supplement.