WASHINGTON (CNN) -- Two presidential candidates are locked in a war of words over Iraq and, to a lesser degree, spelling.

On Friday, Sen. Barack Obama, D-Illinois, referred to a "flack jacket" in a press release defending his "no" vote on Thursday's Iraq war funding bill. Sen. John McCain, R-Arizona, responded with his own release which concludes with the line, "By the way, Senator Obama, it's a 'flak' jacket, not a 'flack' jacket."

The term "flak" refers to the fire from an anti-aircraft gun.

According to Webster's New World Dictionary, the American Heritage Dictionary, and the Oxford English Dictionary, "flack" is an alternate spelling of "flak," though the main listing for the term is under "flak." Two additional dictionaries, the Merriam Webster Dictionary: Home and Office Edition and the Webster's II New Riverside University Dictionary, list only "flak," and do not indicate "flack" as an alternate spelling.

A press spokesman, which incidentally is another possible definition for the term "flack" but not "flak," for the U.S. Army says the military generally does not use either spelling in official written communications, opting instead to refer to specific types of armor or weaponry. The spokesman added that while both spellings are used informally, "flak" is more common.