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 the IBM 704 computer on which the original Lisp
was developed.
The IBM 704 is a footnote in history, but these names are now beloved traditions of Lisp.