In makefiles what do CC and LD stand for?

Names of these variables originate from names of the corresponding tools. Usually the meaning of these abbreviations is the following:

• CC stands for "C compiler" (in GCC abbreviation it is also treated as "compiler collection").
• LD is a linker (comes from "link editor" or from "loader").

These are also commonly used in makefiles (see Implicit variables chapter of GNU Make manual):

• CPP stands for "C preprocessor"
• CXX is a C++ compiler
• AS is an assembly language compiler
• AR is an archive-maintaining program

CC is "C Compiler". LD is "Link Editor". LE was already used to mean "less or equal" in a shell, likely sh. So, per convention, the conflicting character was moved one character forward in the word being abbreviated. Hence LD and DYLD.