忍 is a Logical Aggregate and Phonetic Compound at the same time, formed from two semantic indicators of 心 (literally means the heart or mind, feeling, intention) and 刃 (literally means knife-edge; blade. 刃, which is formed from a pictogram of 刀 with a dot stroke on the left, means to make you aware of the sharpness of the knife.), and 刃 (not rěn but rèn due to the evolution of years of Chinese phonetics ) is also defined as its phonetic component.
忍耐，容忍endure; tolerate; put up with
Lily explains 忍 like this:
忍 is usually cherished as a highly thought virtue by traditional Chinese people. To be a successful man who can make an extraordinary achievement, you must first learn how to endure hardships and swallow insults and humiliations while keeping your true ambitious goals secretly in mind as well. Even someone insults you like thrusting at your heart with a sharp knife, you are not supposed to give an eye for an eye immediately. Instead, you should well repress your hatred to get by (of course, if you could survive the attack and got still alive after that) in order to carry out your big plan in the future. You may know the old Chinese saying that for a gentleman to take revenge, ten years is not too late to wait. You see, in China, revenge is a dish best served cold.