The difference between Instant and Moment

When used as nouns, instant means a very short period of time, whereas moment means a brief, unspecified amount of time.

Instant is also adverb with the meaning: at once.

Instant is also adjective with the meaning: impending.

check bellow for the other definitions of Instant and Moment

Instant as a noun:

A very short period of time; a moment.

Examples:

"She paused for only an instant, which was just enough time for John to change the subject."
Instant as a noun:

A single, usually precise, point in time.

Examples:

"The instant the alarm went off, he fled the building."
Instant as a noun:

A beverage or food which has been pre-processed to reduce preparation time, especially instant coffee.
Instant as a noun:

A day of the current month (abbreviated as: inst.)

Examples:

"In response to your letter of the twenty-first instant..."

Instant as an adjective (dated):

Impending; imminent.
Instant as an adjective (dated):

Urgent; pressing; acute.
Instant as an adjective:

Occurring immediately; immediate; present.
Instant as an adjective:

Lasting for a short moment; momentary; short-lived.
Instant as an adjective:

Very quickly and easily prepared.

Examples:

"instant coffee; instant noodles; instant mashed potato''; instant photo"
Instant as an adjective:

Of the current month (abbreviation inst.).

Examples:

"I refer to your letter of the 16th inst. in regard to traffic disruption."

Moment as a noun:

A brief, unspecified amount of time.

Examples:

"Wait a moment, while I lock the front door."
Moment as a noun:

The smallest portion of time; an instant.
Moment as a noun:

Weight or importance.
Moment as a noun (physics, mechanics):

The turning effect of a force applied to a rotational system at a distance from the axis of rotation. Also called moment of force.
Moment as a noun (historical):

A definite period of time, specifically one-tenth of a point, or one-fortieth or one-fiftieth of an hour.
Moment as a noun (informal):

A petit mal episode; such a spell.
Moment as a noun (colloquial):

A fit; a brief tantrum.
Moment as a noun (math):

An infinitesimal change in a varying quantity; an increment or decrement.
Moment as a noun (math):

A quantitative measure of the shape of a set of points.

Examples:

"If the points represent mass, then the zeroth moment is the total mass, the first moment divided by the total mass is the center of mass, and the second moment is the rotational inertia."