diamond vs piece of ground

diamond and piece of ground both are nouns.

Word	Noun	Adjective	Verb	Adverb
diamond	Yes	No	No	No
piece of ground	Yes	No	No	No

As nouns, piece of ground is a hypernym of diamond; that is, piece of ground is a word with a broader meaning than diamond:

diamond: the area of a baseball field that is enclosed by 3 bases and home plate
piece of ground: an extended area of land

Other hypernyms of diamond include parcel, parcel of land, piece of land, tract.

diamond (noun)	piece of ground (noun)
the area of a baseball field that is enclosed by 3 bases and home plate	an extended area of land
a playing card in the minor suit that has one or more red rhombuses on it
the baseball playing field
a transparent piece of diamond that has been cut and polished and is valued as a precious gem
a parallelogram with four equal sides; an oblique-angled equilateral parallelogram
very hard native crystalline carbon valued as a gem