guide word vs guideword

guide word and guideword both are nouns.

Word	Noun	Adjective	Verb	Adverb
guide word	Yes	No	No	No
guideword	Yes	No	No	No

As nouns, guide word and guideword are synonyms defined as:

guide word and guideword: a word printed at the top of the page of a dictionary or other reference book to indicate the first or last item on that page

Other synonyms of guide word include catchword.

guide word (noun)	guideword (noun)
a word printed at the top of the page of a dictionary or other reference book to indicate the first or last item on that page	a word printed at the top of the page of a dictionary or other reference book to indicate the first or last item on that page