Word to the wise is a shortened version of the phrase a word to the wise is sufficient. Bascially meaning that I’ll say one word and you will be wise enough to know exactly what I’m talking about. There is a connotation of the information being passed in a secret way. It is sometimes used for comedic effect by sharing common sense information.
Even when the word is a long sentence, the idiom should not be phrased words to the wise, since the meaning of the idiom is that one word will suffice.
Side note: the original Latin phrase was also similarly shortened.
Examples
And as India’s economy continues to grow, and trade with Canada increases rapidly (the two countries have vowed to expand annual bilateral trade to at least $15-billion by next year), the boom registers strongest in Mumbai, the subcontinent’s financial capital—which, word to the wise, is almost always known locally by its old name, Bombay. [The Globe and Mail]
A final word to the wise: political independence does not always bring fulfilment and contentment. Fenton people know this better than most, having secured it several times and tossed it away in as many turns. [Stoke Sentinel]
A word to the wise – the weightlifting isn’t done with normal gym weights, it’s the full Olympic-style “clean and jerk” and one over-enthusiastic FN reader managed to put his neck out for a week after his first session. [The Tally]
Just a little word to the wise: “Never try to outrun a Mounted Patrol or K9 Officer.” You won’t win. [Pioneer Press]