Feature rabbit: a feature that initially appears to be one feature but after being worked on ends up having lots of other software features as a part of it. Feature rabbits breed when managers want to try and sneak extra work in their initial request, or often if a critical point was not articulated or recorded during the initial feature estimation.
Rabbit hole: a feature or bug fix that takes way longer than the initial estimate because it turns out implementation has greater complexity than initially understood.
Christmas tree: a software project that lots of stakeholders try and put their own features on. Christmas trees tend to lack product owners.
Tool tax: the time you pay to learn and use an additional tool in relation to your software projects. If a new tool saves you time it becomes worth it, but often each tool increases the tuition a newcomer must pay to work on your project.
Tuition: the one time cost you have to pay in order to work on a project because you need to learn a new technology.