誓 and 折 don't sound similar in modern Mandarin due to historical phonetic changes. They were more similar
in older Chinese.
Character Evolution
BronzeLate Western Zhou~800 BCBronzeLate Western Zhou~800 BCBronzeLate Western Zhou~800 BCBronzeLate Spring and Autumn~500 BCSealShuowen~100 ADClericalEastern Han25-220 ADRegularModern