(one's) secret weapon

Some person, thing, or element at one's disposal that provides one with a distinct advantage, especially because it is not known or discussed widely (or at all). The new Flapple and Spikerosoft computers are largely equal in most areas hardware-wise, but the latter's incredibly intuitive operating system could end up being its secret weapon. Our support among younger voters is going to be our secret weapon this election. The team's incredible new quarterback is going to be their secret weapon going into this season.

be a double-edged sword

To be something that can be both beneficial and problematic. Going back to school was a double-edged sword for Pam. On the one hand, it widened her career prospects, but, on the other hand, she was in a lot of debt when she graduated. Intelligence is a double-edged sword. Things may come easy to you, but people will always expect more. This meeting is a double-edged sword—it's a great chance to get the firm wider exposure, but we're just not prepared enough for it.

be a double-edged weapon

To be something that can be both beneficial and problematic. Going back to school was a double-edged weapon for Pam. On the one hand, it widened her career prospects, but, on the other hand, she was in a lot of debt when she graduated. Intelligence is a double-edged weapon. Things may come easy to you, but people will always expect more. This meeting is a double-edged weapon—it's a great chance to get the firm wider exposure, but we're just not prepared enough for it.

weapon of choice

1. Literally, a weapon one prefers to use during combat. The Tommy Gun became the infamous weapon of choice for gangsters during the Prohibition era. The assassin was proficient in many deadly weapons, but her weapon of choice was the stiletto.

2. A tool, tactic, method, etc., considered the most effective or ideal in a given situation. Strikes have always been the weapon of choice for labor unions looking to achieve better working conditions. Text messages have increasingly become a weapon of choice for political campaigns in recent years. As a parent of two messy kids, let me tell you, EverClean Laundry Detergent is my weapon of choice when it comes to keeping clothes looking like new!

weapon of mass destruction

Any weapon, especially one that is nuclear, chemical, or biological in nature, that can be used to end lives and cause damage on a very large scale. Popularized in recent times by the administration of US President George W. Bush in relation to the invasion of Iraq in 2003. Sometimes used for hyperbolic, sarcastic, or humorous effect. The report concluded that the country had been manufacturing weapons of mass destruction in order to cause as much death and destruction as possible. Ugh, crack a window, dude—that fart was a weapon of mass destruction!

be a double-edged ˈsword/ˈweapon

be something that has both advantages and disadvantages: This new ‘miracle diet’ is a double-edged sword — it’ll make you lose weight fast but you may have some unpleasant side effects.

secret weapon

A clandestine item or mode of attack unknown to the enemy. The term came into wide use during World War II, when it was rumored that Hitler was going to launch a powerful secret weapon against Great Britain. Subsequently the term was applied to pilotless planes, robot bombs, rockets, and nuclear bombs. Thereafter it entered the civilian vocabulary, where it is used in sports (“Bill’s second serve, stronger than the first, is his secret weapon”) and numerous other activities. Edith Simon had it in The Past Masters (1953): “See the candid camera at work, that misnamed secret weapon.”

weapons of mass destruction

Also, WMD. Weapons that can greatly harm or kill large numbers of people and/or severely damage man-made structures or the biosphere. The term was first used by the Archbishop of Canterbury in 1937 with reference to the aerial bombardment of Guernica, Spain. Less than a decade later, the term was applied to nonconventional weapons, specifically nuclear weapons. During the Cuban missile crisis of 1962, the term was used by President John F. Kennedy, referring to nuclear missiles. Fearing Iraq’s use of nuclear weapons, the alleged existence of such weapons became the main justification for the 2003 invasion of that country. By then, the term was so well known and so often abbreviated that it was on its way to clichédom.