'Guyanese' originates from English, specifically the place-name 'Guyana' combined with the adjectival suffix '-ese'.

'Guyana' was recorded in Spanish and Portuguese forms 'Guayana'/'Guiana', ultimately from an indigenous Amerindian word 'Guiana' meaning 'land of many waters'; the suffix '-ese' entered English via Italian and Portuguese and is ultimately related to Late Latin '-ensis' meaning 'originating in'.

Initially it meant 'of or from Guyana', and this meaning has been retained in modern usage.