wordplay - Four-words (----||||)

Four-words :
My first is indivisible , but not really.
My second is a cloak worn by men , but in ancient Rome.

My third is a cruel wicked person , but not a human.
My fourth is about 20 quires , but in reverse.

I was not allowed a very short title for this puzzle , but I was able to add a clue to make it cross the 15-letters-minimum limit for titles.

Answer

My first is indivisible, but not really.

The word ATOM means "indivisible" in ancient Greek, but atoms aren't really indivisible since they have protons, neutrons, quarks, etc. inside them.

My second is a cloak worn by men, but in ancient Rome.

A TOGA

is the answer there.

My third is a cruel wicked person, but not a human.

An OGRE.

My fourth is about 20 quires, but in reverse.

20 quires

form a ream, so the answer to this is MAER.

And the full answer is:

A T O M
T O G A
O G R E
M A E R

Lovely puzzle!