easily set on fire; combustible; inflammable.
Origin of flammable
1805–15; < Latin flammā(re) to set on fire + -ble
Dictionary.com Unabridged Based on the Random House Unabridged Dictionary, © Random House, Inc. 2019
liable to catch fire; readily combustible; inflammable
Flammable and inflammable are interchangeable when used of the properties of materials. Flammable is, however, often preferred for warning labels as there is less likelihood of misunderstanding (inflammable being sometimes taken to mean not flammable). Inflammable is preferred in figurative contexts: this could prove to be an inflammable situation
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
Online Etymology Dictionary, © 2010 Douglas Harper