Dictionary.com
definitions

unearned increment

noun
  1. the increase in the value of property, especially land, due to natural causes, as growth of population, rather than to any labor or expenditure by the owner.

Origin of unearned increment

First recorded in 1870–75
Dictionary.com Unabridged Based on the Random House Unabridged Dictionary, © Random House, Inc. 2018
British Dictionary definitions for unearned increment

unearned increment

noun
  1. a rise in the market value of landed property resulting from general economic factors
Collins English Dictionary - Complete & Unabridged 2012 Digital Edition © William Collins Sons & Co. Ltd. 1979, 1986 © HarperCollins Publishers 1998, 2000, 2003, 2005, 2006, 2007, 2009, 2012