The difference between Giant and Prodigious

When used as adjectives, giant means very large, whereas prodigious means very big in size or quantity.

Giant is also noun with the meaning: a mythical human of very great size.

check bellow for the other definitions of Giant and Prodigious

Giant as a noun:

A mythical human of very great size.
Giant as a noun (mythology):

Specifically, any of the gigantes, the race of giants in the Greek mythology.
Giant as a noun:

A very tall person.
Giant as a noun:

A tall species of a particular animal or plant.
Giant as a noun (astronomy):

A star that is considerably more luminous than a main sequence star of the same temperature (e.g. red giant, blue giant).
Giant as a noun (computing):

An Ethernet packet that exceeds the medium's maximum packet size of 1,518 bytes.
Giant as a noun:

A very large organisation.

Examples:

"The retail giant is set to acquire two more struggling high-street chains."
Giant as a noun:

A person of extraordinary strength or powers, bodily or intellectual.
Giant as a noun:

jotun

Prodigious as an adjective:

Very big in size or quantity; gigantic; colossal; huge.
Prodigious as an adjective:

Extraordinarily exciting or amazing.
Prodigious as an adjective (obsolete):

Ominous, portentous.
Prodigious as an adjective:

Monstrous; freakish.