What is the difference between a model, a replica and a scale model?

Any terms (especially in modelling) that are used interchangeably are undoubtedly the starting point for many conversations and debates. The truth is, it doesn't really matter in the grand scheme of things which terminology you use as most modellers will understand what you mean even if the odd word is used out of place. But to satisfy the natural curiosity of the modeller's mind, here are the official definitions of model, replica and scale-model according to the Cambridge English Dictionary.

Model - "A physical object, usually smaller than the real object, that is used to represent something".

Replica - "An exact copy of an object".

Scale model - Surprisingly, scale model doesn't appear as a sub-definition of scale in the dictionary despite being a recognised term for many decades, however, the word scale is defined as follows: "The relation between the real size of something and its size on a map, model, or diagram"

The obvious conclusion to take from this is that modellers have got it spot on when describing the miniature railway engines, planes, boats and buildings they create as 'scale models' which would indicate the recreation of an object in a different size to the original that represents but is not an exact copy of it. But does the word replica deserve a place in the hobby? Maybe not, because to be an exact copy of something surely it must be the same size and have the internal workings and interior present and perform the same function as the original. It looks like the debate continues!