1. Map isn't "also a data structure", the data structure is a way to implement a mapping function. There is no conceptual difference between code and data (for an example, see http://en.m.wikipedia.org/wiki/Cons#Not_technically_fundamen...)

2. cadr is relatively easy, if you know your assembly (http://en.m.wikipedia.org/wiki/Car_and_cdr#Etymology) :-)

And math has locally defined terms because one cannot give every concept a unique short meaningful memorable name. That is no different in computer science, where 'integer' can include negative numbers or not, may or may not wrap around, can be any number of bits or potentially unlimited, may include minus zero, etc.