dog days vs canicular days

dog days and canicular days both are nouns.

Word	Noun	Adjective	Verb	Adverb
dog days	Yes	No	No	No
canicular days	Yes	No	No	No

As nouns, dog days and canicular days are synonyms defined as:

dog days and canicular days: the hot period between early July and early September; a period of inactivity

Other synonyms of dog days include canicule.

dog days (noun)	canicular days (noun)
the hot period between early July and early September; a period of inactivity	the hot period between early July and early September; a period of inactivity