idiom, expression

(ひょうげん) A more broad word meaning simply, ‘expression.’ Freedom of expression. What the artist was trying to express with this painting. Etc. Is this ever used about idioms?
(かんようく) An idiom. For example, 明日がまちどおし.(’I can’t wait for tomorrow!’)
(かくげん) A proverb
ことわざ A proverb   $$$
(ほうげん) A somewhat more informal word for dialect- i.e. all the idioms of a particular region.
(xxxべん) Dialect.