unique
The assumption to design heat exchanger is that it must be a shell and tube device. This device must allow the transfer of heat from one fluid to another without mixing the two fluids.
A drip-proof machine is one where the design of the various vents does not allow water and other contaminants that fall on the machine to enter the machine.
A heatpump that only has one stage of heat and one stage of cool.
aircraft engines only move one way... no reverse
An example of a tool that only has 2 parts is a hammer because the handle and the top medal part
It will only fit one way.It will only fit one way.
Illeghenices But there is a better one.
It is one word, safeguard (to protect, a protective act or design).
Many people believe that creationism is a one word synonym for intelligent design. Though this is not true, I hope it may be the answer you are looking for.
Comestible (fit to eat or drink), potable is fit to drink
monograph
A Custom Chandelier is one that is made to fit a unique design or circumstance. A chandelier built by a manufacturer to dimensions or design that is not readily available in the marketplace.
The person would be either qualified, eligible, or electable.
You can only fit 32 eggs in your mouth at one time.
The only one that comes to mind is 'amble' which is OK for wander but does not fit well as an alternative meaning for roll.
they were the only one
The word, elapse, would fit your description.