Celtis australis vs hackberry

Celtis australis and hackberry both are nouns.

Word	Noun	Adjective	Verb	Adverb
Celtis australis	Yes	No	No	No
hackberry	Yes	No	No	No

As nouns, hackberry is a hypernym of Celtis australis; that is, hackberry is a word with a broader meaning than Celtis australis:

Celtis australis: bright green deciduous shade tree of southern Europe
hackberry: any of various trees of the genus Celtis having inconspicuous flowers and small berrylike fruits

Other hypernyms of Celtis australis include nettle tree.

Celtis australis (noun)	hackberry (noun)
bright green deciduous shade tree of southern Europe	small edible dark purple to black berry with large pits; southern United States
	any of various trees of the genus Celtis having inconspicuous flowers and small berrylike fruits