You should always use the word which is common among the users, no matter if it is the technically correct one or not.
In Why the electronic land registry failed, Lauesen gave a very vivid example of this. This is a story of a large system which had to be made mandatory for use in real estate purchases in the whole of Denmark. The requirements were gathered from a few experts, among them an old judge specializing in real estate law. This judge made a very big point of using the proper legal terms for everything. As the requirements engineers had no access to real users and no political power to overthrow the judge's wishes, they put these terms into the specification.
In the post mortem, the author identifies this as one of the large problems with the project. The users of the system - who were real estate agents, not lawyers - had absolutely no idea what these terms are. They were completely confused and could not even start working with the system. In the end, the whole project flopped.
This was not the only usability sin committed in this project. The paper accompanying the conference talk is a worthy read (and probably explains it better - I don't even remember it well enough to be sure I got all details right), if it is not available without a paywall, the author may give you a personal copy on request.
But in general, this is a good lesson. If one of your users pushes for a non-intuitive word to be used in the interface, where other users will be confused, don't give in. If it is a system where all users will use this one word, even if technically wrong, use it. They really need their own language there.
Citation for the paper: Lauesen, Soren. "Why the electronic land registry failed." Requirements Engineering: Foundation for Software Quality. Springer Berlin Heidelberg, 2012. 1-15.
Here is an excerpt describing the situation above:
How do you register a condominium deed? There were several options in the menu: Single-family housing, cooperative apartment, farm – but no condominiums.
The professionals were stuck and called the e-LR hotline. It was busy, so they might wait for an hour and then try the next day at a different time. It might take three weeks to succeed. Once they got through, there was an immediate reply: Select single-family housing – it includes condominiums. Since hotline had got this question frequently, one might wonder why developers didn't change the menu. The reason was that the judge in charge of the entire project refused: the law was clear and the term single-family housing covered also condominiums.
Amazingly, the Land Registry was not aware that the essential waiting time was three weeks. To his staff, it looked as nobody waited for more than an hour.