accretion

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.

accretion Oxford Dictionary of English