Saint Vincent and the Grenadines
noun: Saint Vincentian(s) or
Vincentian(s)
adjective: Saint Vincentian or Vincentian

Samoa
noun: Samoan(s)
adjective: Samoan

San Marino
noun: Sammarinese (singular and plural)
adjective: Sammarinese

Sao Tome and Principe
noun: Sao Tomean(s)
adjective: Sao Tomean

Saudi Arabia
noun: Saudi(s)
adjective: Saudi or Saudi Arabian

Senegal
noun: Senegalese (singular and plural)
adjective: Senegalese

Serbia
noun: Serb(s)
adjective: Serbian

Seychelles
noun: Seychellois (singular and plural)
adjective: Seychellois

Sierra Leone
noun: Sierra Leonean(s)
adjective: Sierra Leonean

Singapore
noun: Singaporean(s)
adjective: Singapore