I'm reading McCarthy's paper Recursive Functions of Symbolic Expressions And Their Computation by Machine, where when the author describes the machine implementation of lists, he writes this:
a. Representation of S-Expressions by List Structure. A list structure is a collection of computer words arranged as in figure 1a or 1b. Each word of the list structure is represented by one of the subdivided rectangles in the figure. The left box in the rectangle represents the address field of the word and the right box represents the decrement field. An arrow from a box to another rectangle means that the field corresponding to the box contains the location of the word corresponding to the other rectangle.
From further reading it isn't clear why would he use the word "decrement" to mean "a pointer to a memory location where the data associated with the given list element is stored". It doesn't exactly translate into "dereference" as used today when describing languages s.a. C, but if, in C terms, you were to treat the contents of "decrement" field as a pointer, and then dereference it, you'd get the value of the element.
So, why "decrement"? Was something really decremented? Was it due to some particular features of memory layout of IBM 704?