The difference between Insubstantial and Massive

When used as adjectives, insubstantial means lacking substance, whereas massive means of or pertaining to a large mass.

Massive is also noun with the meaning: a homogeneous mass of rock, not layered and without an obvious crystal structure.

check bellow for the other definitions of Insubstantial and Massive

Insubstantial as an adjective:

Lacking substance; not real or strong.

Examples:

"The bridge was insubstantial and would not safely carry a car."

Massive as an adjective:

Of or pertaining to a large mass; weighty, heavy, or bulky.

Examples:

"A massive comet or asteroid appears to have ended the era of the dinosaurs."
Massive as an adjective:

Much larger than normal.

Examples:

"Compared to its counterparts from World War II, the Abrams main battle tank is truly massive."
Massive as an adjective:

Of great significance or import; overwhelming.

Examples:

"The enlightenment comprises massive shifts in many areas of Western thought."
Massive as an adjective (mineralogy):

Not exhibiting crystal form.
Massive as an adjective:

Of particularly exceptional quality or value; awesome.

Examples:

"Did you see Colbert last night? He was massive!"
Massive as an adjective (colloquial, informal, Ireland):

outstanding, beautiful

Examples:

"Your dress is massive, love. Where did you get it?"
Massive as an adjective (informal):

To a very great extent; total, utter.
Massive as an adjective (physics):

(of a particle) Possessing mass.

Examples:

"Some bosons are massive while others are massless."

Massive as a noun (mineralogy):

A homogeneous mass of rock, not layered and without an obvious crystal structure.

Examples:

"karst massives in western Georgia"
Massive as a noun (slang):

A group of people from a locality, or sharing a collective aim, interest, etc.

Examples:

"Big up to the Croydon massive!"