忍耐
rěnnài · HSK 7
to endure; to put up with; to exercise patience
忍 = blade (刃) over heart (心) = endure; 耐 = withstand
Both characters mean to bear up, so 忍耐 stacks them for emphasis: endurance, patience, putting up with hardship. The 忍 half literally sets a blade above the heart and holds steady; 耐 adds the sense of withstanding strain over time.
忍 — blade 刃 (phonetic) + heart 心 (semantic)
忍 is a semantic-phonetic compound: 心 'heart' below gives the meaning, while 刃 'blade' above provides the sound. The image of a blade over the heart vividly suggests enduring pain or restraining oneself, hence the meanings 'endure, bear, be patient'.
耐 — 而 (beard) + 寸 (hand/rule)
Originally depicted shaving off a beard (而) by hand (寸) as a minor punishment in ancient China. The sense shifted from 'enduring this shame' to the broader meaning 'to endure, bear, withstand.' Today 耐 commonly means patient or resistant, as in 耐心 (patience).