This question is specifically about The Cambridge Grammar of the English Language by Huddleston and Pullum.
Here's CGEL's definition of word:
In order to avoid possible misunderstanding we will restrict the term word to the syntactically-oriented sense, so that hard and harder are different words, and likewise are and is. (Page 27)
How CGEL defines noun is not so clear, but from the following distinction between proper noun and proper name, CGEL seems to define noun as a single word:
In their primary use proper names normally refer to the particular entities that they name: in this use they have the syntactic status of NPs.
Proper nouns, by contrast, are word-level units belonging to the category noun. Clinton and Zealand are proper nouns, but New Zealand is not. (Page 516)
In the following excerpt, CGEL seems to define compound noun as a single word (Page 448):
But CGEL also classifies a two-word unit such as full stop as a compound noun (Page 451):
(1) Does CGEL define the term word as a lexical unit having no space within when written or printed?
(2) Does CGEL define the term noun as a single word?
(3) Since CGEL says full stop is a compound noun, does the term compound noun as defined in CGEL include not only a single-word unit but also a multiple-word unit?
(4) If answers to the above questions are all 'yes', how can you say the term noun is a single-word unit and at the same time that the term compound noun can be a multiple-word unit?