sheath sheath /ˈʃiːθ/

noun

1. () A protective covering (as for a knife or sword)  ( sheath )
   a protective covering (as for a knife or sword)
    He safely stored his knife in a leather sheath.
   He safely stored his knife in a leather sheath.
   
   
2. () A dress suitable for formal occasions  ( cocktail dress , sheath )
   a dress suitable for formal occasions
    She wore a black sheath dress to the formal dinner.
   She wore a black sheath dress to the formal dinner.
   
   
3. () An enveloping structure or covering enclosing an animal or plant organ or part  ( case , sheath )
   an enveloping structure or covering enclosing an animal or plant organ or part