All 4 Uses

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Flags of Our Fathers
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The Japanese in Nanking killed even more than the atomic bombs later would.†
Chpt 3. *

atomic = related to the smallest part of any material that cannot be broken up by chemical means
Charles Sweeney, who later dropped the atomic bomb on Nagasaki, would write that his Catholic mother allowed only two images to be hung on the family's dining-room wall: Jesus and FDR.†
Chpt 12.
A two-front world war and the secret and fabulously expensive building of the atomic bomb had drained the national coffers.†
Chpt 15.
"The decision whether or not to use the atomic bomb to complete the surrender of Japan was never an issue," Churchill later wrote.†
Chpt 17.

Definitions:

(1) (atom)
the smallest part of any material that cannot be broken up by chemical means; comprised of a nucleus of protons and neutrons surrounded by orbiting electrons
(2) (meaning too rare to warrant focus)