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

Slovakia
noun: Slovak(s)
adjective: Slovak

Slovenia
noun: Slovene(s)
adjective: Slovenian

Solomon Islands
noun: Solomon Islander(s)
adjective: Solomon Islander