apart

Apart is defined as a whole thing being broken down into units.

(adverb)

A very old building that is rotting with pieces falling off of it is an example of a building that is falling apart.

The definition of apart are things that are not together in any way, such as things separated by time or distance.

(adverb)

A child born three years after his brother is an example of a child who is three years apart from his brother.

See apart in Webster's New World College Dictionary

adverb

Origin: ME < OFr a part < L ad, to, at + partem, acc. of pars, a side, part

adjective

separated; not together: used in the predicate

See apart in American Heritage Dictionary 4

adverb

a. At a distance in place, position, or time: railings spaced two feet apart; born three years apart.
b. Away from another or others: grew apart over the years; decided to live apart.
In or into parts or pieces: split apart.
One from another: I can't tell the twins apart.
Aside or in reserve, as for a separate use or purpose: funds set apart for the project.
As a distinct item or entity: Quality sets it apart.
So as to except or exclude from consideration; aside: All joking apart, I think you're wrong.