Mat 12:36 But I say to you, That every idle word that men shall speak, they shall give account for on the day of judgment.

Another good play on words in the Greek is lost in English translation.

"Idle" is argos, which means "not working the ground," "lazy," and "idle" when applied to people, but when applied to things (like words) "lying idle," "yeilding no return," and "fruitless." Again, this word is very consistent with Christ's message about "good" being "useful" and 'bad" being "useless.

"Word" is not the Greek term (logos) usually translated as "word.' Instead, it is rhêma, which means "that which is spoken," but more in the sense of a "saying," or "phrase."

"Give" is from apodidômi, which means "to give back," "to restore," and "to deliver." It has the economic sense of "to sell" or "to give something for one's own profit."

"Account" is actually the normal term for "word," logos. Logos is usually translated in the Gospels as "word," but in Greek it has a wide variety of meanings. It means "a computation," "a reckoning," and "value." It is also "an explanation," "an argument," or "a rule or principle of law." While rhema can be thought of as just words, logos means reasoning as much as speaking.

"The day of judgment" is hemera (day) krisis (trial, selection, separating).

So Christ is saying: Every form of lazy, profitless chatter will have to be logically justified in the future.