'Allegheny' originates from the Lenape (Delaware) language, likely from a word such as 'oolikhanna' or a similar Algonquian form, where the element meant 'river' or 'fine/beautiful river.'

'Allegheny' entered English usage via early colonial maps and writings (17th–18th century), appearing in forms like 'Alleghene' and eventually stabilizing as 'Allegheny' for the river and associated mountains/places.

Initially it referred primarily to the Allegheny River (a watercourse), but over time the name extended to the surrounding highlands and ranges now called the Alleghenies (mountain region).