Node:Strange Names, Next:car & cdr, Previous:car cdr & cons, Up:car cdr & cons
The name of the cons function is not unreasonable: it is an
abbreviation of the word `construct'. The origins of the names for
car and cdr, on the other hand, are esoteric: car
is an acronym from the phrase `Contents of the Address part of the
Register'; and cdr (pronounced `could-er') is an acronym from
the phrase `Contents of the Decrement part of the Register'. These
phrases refer to specific pieces of hardware on the very early
computer on which the original Lisp was developed. Besides being
obsolete, the phrases have been completely irrelevant for more than 25
years to anyone thinking about Lisp. Nonetheless, although a few
brave scholars have begun to use more reasonable names for these
functions, the old terms are still in use. In particular, since the
terms are used in the Emacs Lisp source code, we will use them in this
introduction.