For me, the term 'airliner' conjures up an image of a passenger jet that is capable of hosting a large number of passengers¹ but I'm finding it difficult to source a reputable definition or etymology despite the term has been sourced int the early 20th century.
Since the term has been in use since 1908, jet as in jet airliner may be inferred by the modern user but it obviously wasn't part of the original definition.
The word itself would seem to indicate that airliner refers to an aircraft used by an airline (a company that provides air travel for the public), but would that extend to bush pilots with small prop-driven Cessnas or passenger helicopters?
airliner - A large passenger aircraft. A large plane for carrying passengers: a commercial/commuter airliner
source: Cambridge English Dictionary
airliner - An airplane operated by an airline
source: Merriam-Webster Dictionary
Is this an 'airliner'? How many passenger seats need to be added before it becomes one?
(image courtesy of The Bush Pilot Company)
The term seems so vague that even the airliner tag on this site only uses 'large' to define size or capacity.
Some reference work definitions include cargo aircraft but the predominant emphasis seems to be on passenger aircraft with no upper or lower limit criteria.
I suppose that this term could be relative to the observer or situation but if the term 'airliner' was used in FAA regulations then I'm sure there must be an appendix somewhere that provides a definition. My research has come up empty.
Apologies if this is a dumb question and the term is intentionally meant be vague with only 'large aircraft' or 'many passenger' as criteria. Given proper references as support, that could be an answer.
¹ This previous question got me wondering exactly what was the criteria before any aircraft could be called an 'airliner'.