Longman Dictionary of Contemporary English
Douglas Harper's Etymology Dictionary
Wiktionary
n. A competition for military supremacy between two powers, especially for the most weapons and the best military technology.
WordNet
n. a competition between nations to have the most powerful armaments
Wikipedia
An arms race, in its original usage, is a competition between two or more parties to have the best armed forces. Each party competes to produce larger numbers of weapons, greater armies, superior military technology, etc. in a technological escalation.
International conflict specialist Theresa Clair Smith, defines the term as "the participation of two or more nation-states in apparently competitive or interactive increases in quantity or quality of war material and/or persons under arms."
The term is also used to describe a competitive situation, in which the purpose is only to be more successful than one's competitors.
Usage examples of "arms race".
It's only the rotten Americans and their arms race who stand in the way but soon we'll force even them to lay down their arms and we'll all be equal.
The Golden Asaleny's got himself a fleet of aircraft, which he thinks gives him an upper hand in the arms race.
They'll start the arms race all over again or even pull a pre-emptive strike!
Nixon ended the war, opened the door to dealings with China, capped the arms race, and passed the first serious environmental legislation in seventy years.
Already the international web that had precipitated World War I, financed both the Bolshevik Revolution and the rise of Hitler, manufactured the Middle East and Southeast Asian crises of later years, contrived for a whole world to fund its own blackmail through the nuclear arms race, and been behind a long list of other interesting things found recorded in great detail inside JEVEX, was well on its way to being broken up for good.
That smugness was eroded when the Soviets exploded their own nuclear device, and the arms race was on.