rule of thumb vs guidepost

rule of thumb and guidepost both are nouns.

Word	Noun	Adjective	Verb	Adverb
rule of thumb	Yes	No	No	No
guidepost	Yes	No	No	No

As nouns, rule of thumb and guidepost are synonyms defined as:

rule of thumb and guidepost: a rule or principle that provides guidance to appropriate behavior

Other synonyms of rule of thumb include guideline.

rule of thumb (noun)	guidepost (noun)
a rule or principle that provides guidance to appropriate behavior	a rule or principle that provides guidance to appropriate behavior
	a post bearing a sign that gives directions or shows the way