Dictionary.com
definitions

struggle for existence

noun
  1. the competition in nature among organisms of a population to maintain themselves in a given environment and to survive to reproduce others of their kind.

Origin of struggle for existence

First recorded in 1820–30
Dictionary.com Unabridged Based on the Random House Unabridged Dictionary, © Random House, Inc. 2018
British Dictionary definitions for struggle for existence

struggle for existence

noun
  1. (not in technical usage) competition between organisms of a population, esp as a factor in the evolution of plants and animalsSee also natural selection
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