1. Too sacred to be uttered
   - ineffable, unnameable, unspeakable, unutterable 
2. Not capable of being said
   - unspeakable

See also: sacred

• Sir Winston Leonard Spenser Churchill
• Sir Yehudi Menuhin
• Sirach
• Siracusa
• Siraj-ud-daula
• SIRC
• sirdar
• sire
• siree
• siren
• siren call
• siren song
• Sirenia
• sirenian
• sirenian mammal
• Sirenidae
• siriasis
• siris
• siris tree
• Sirius
• sirloin
• sirloin steak
• sirloin tip
• sirocco
• sirrah