It is curious to track the path by which the word `argument' came to have two different meanings, one in mathematics and the other in everyday English. According to the Oxford English Dictionary, the word derives from the Latin for `to make clear, prove'; thus it came to mean, by one thread of derivation, `the evidence offered as proof', which is to say, `the information offered', which led to its meaning in Lisp. But in the other thread of derivation, it came to mean `to assert in a manner against which others may make counter assertions', which led to the meaning of the word as a disputation. (Note here that the English word has two different definitions attached to it at the same time. By contrast, in Emacs Lisp, a symbol cannot have two different function definitions at the same time.)
Actually, you can
cons an element to an atom to produce a dotted pair. Dotted
pairs are not discussed here; see section `Dotted Pair Notation' in The GNU Emacs Lisp Reference Manual.