衰减
shuāi jiǎn · HSK 7
to weaken
📉 衰 decline + 减 reduce = a signal that declines and reduces, i.e. attenuates
衰 (shuāi) means to decline or grow weak; 减 (jiǎn) means to subtract or reduce. Together they name the gradual drop-off of a signal, force, or wave over distance or time.
减 — water 氵 + 咸 (xián, all/salty)
A semantic-phonetic compound. The water radical 氵 gives the meaning, originally suggesting water decreasing or draining away, while 咸 supplies the sound (jiǎn shifted from xián). From 'water lessening' the sense broadened to 'reduce, subtract, diminish' in general use.