say it: GAHYD-lahyn
guideline is a noun meaning "a light line that is used in lettering to help align the letters". It carries 3 recorded senses.
a light line that is used in lettering to help align the letters
a rule or principle that provides guidance to appropriate behavior
Forms marked · are formed by the regular rule rather than recorded in the source data. English keeps a few hundred irregulars and the rest follow the pattern, so the rule is right far more often than not — but it is a rule, and the mark says so.
Definitions, synonyms and semantic relations for guideline come from Princeton University’s WordNet. The pronunciation comes from the CMU Pronouncing Dictionary. Commonness is measured against a corpus of everyday English. Full sources and licences.