loading vs millstone

loading and millstone both are nouns.

Word	Noun	Adjective	Verb	Adverb
loading	Yes	No	No	No
millstone	Yes	No	No	No

As nouns, millstone is a hyponym of loading; that is, millstone is a word with a more specific, narrower meaning than loading:

Other hyponyms of loading include burthen, dead load, live load, superload, overburden, overload, overload.

loading (noun)	millstone (noun)
the labor of putting a load of something on or in a vehicle or ship or container etc.	one of a pair of heavy flat disk-shaped stones that are rotated against one another to grind the grain
goods carried by a large vehicle	any load that is difficult to carry
weight to be borne or conveyed	(figurative) something that hinders or handicaps
a quantity that can be processed or transported at one time
the ratio of the gross weight of an airplane to some factor determining its lift