As weird as it seems, a
meito can be any named weapon, they don't even need to be blades. Even blunt weapons like Kaido's Hassaikai and Yamato's Takeru are meitos (even Kanjuro's brush btw

). They also don't need to have a grade to be considered meitos, but Takeru is in the "unknown grade" section of Road to Laugh Tale's page about "blades" and Oda already said on
SBS Vol. 100 that Kaido's Hassaikai would be legendary if he left it behind, so this pretty much confirms that any melee weapon can be graded.
(Road to Laugh Tale, Vol. 2)