Definition of baseplate:
(n) :
A solid piece of material that has enough strength and sturdiness to serve as the surface to which other things are attached to be supported.
(n) :
(rail transport) Synonym of tie plate.
(v) :
(transitive) To fit with a baseplate.
(v) :
(transitive, US, logistics) To provide (the vehicles within a fleet) with license plates registered as a batch in a particular state.