cave; cavern; den; grotto
residence of a retired emperor; dwelling of a former emperor; retired emperor; former emperor; emperor emeritus
service tunnel (cables, gas, etc.)
venous sinus; sinus venosus
dongxiao (Chinese bamboo flute similar to a shakuhachi)
sand martin (Riparia riparia)
sinoatrial; (arch.) inner bedroom; (arch.) brothel
sick sinus syndrome; sinus node dysfunction; SSS
(animal) whiskers; vibrissae
sinus node; sinoatrial node
sinus arrhythmia; irregular heartbeat