rebel (adj.)

c. 1300, from Old French rebelle "stubborn, obstinate, rebellious" (12c.) and directly from Latin rebellis "insurgent, rebellious," from rebellare "to rebel, revolt," from re- "opposite, against," or perhaps "again" (see re-) + bellare "wage war," from bellum "war" (see bellicose).

rebel (v.)

mid-14c., from Old French rebeller (14c.), from Latin rebellare "to revolt" (see rebel (adj.)). Related: Rebelled; rebelling.

rebel (n.)

"person who makes war on his country for political motives," mid-14c., from rebel (adj.). Meaning "supporter of the American cause in the War of Independence" is from 1775; sense of "supporter of the Southern cause in the American Civil War" is attested from April 15, 1861. Rebel yell in an American Civil War context attested from 1862, but the thing itself is older and was said to have been picked up by (then) southwestern men in their periodic wars against the Indians.

The Southern troops, when charging or to express their delight, always yell in a manner peculiar to themselves. The Yankee cheer is more like ours; but the Confederate officers declare that the rebel yell has a particular merit, and always produces a salutary and useful effect upon their adversaries. A corps is sometimes spoken of as a 'good yelling regiment.' [A.J.L. Fremantle, "The Battle of Gettysburg and the Campaign in Pennsylvania," in Blackwood's Edinburgh Magazine, Sept. 1863]

Others are reading

Definitions of rebel from WordNet
rebel (v.)
take part in a rebellion; renounce a former allegiance;
Synonyms: arise / rise / rise up
rebel (v.)
break with established customs;
Synonyms: renegade
rebel (n.)
a person who takes part in an armed rebellion against the constituted authority (especially in the hope of improving conditions);
Synonyms: insurgent / insurrectionist / freedom fighter
rebel (n.)
someone who exhibits great independence in thought and action;
Synonyms: maverick
Rebel (n.)
`Johnny' was applied as a nickname for Confederate soldiers by the Federal soldiers in the American Civil War; `greyback' derived from their grey Confederate uniforms;
Synonyms: Reb / Johnny Reb / Johnny / greyback