On the q.t. means doing something secretly. The q.t. in the phrase on the q.t. is an abbreviation of the word quiet. The term originated in the mid-1800s. There is some debate on whether the phrase on the q.t. is of American or English origin.
At this time, the oldest examples of the phrase on the q.t. are found in British media. However, the Americans had a penchant in the 1800s for coining abbreviations.
While the Oxford English Dictionary lists the phrase with lowercase letters and periods (on the q.t.), it is nearly always rendered with uppercase letters and without periods, as in on the QT.
Examples
Although it’s still hush-hush, sotto voce and strictly on the QT, the Bandera County Courier has learned about possible plans for the site of the old Cabaret Dance Hall. (The Bandera County Courier)
Not a word about the Attorney General Loretta Lynch meeting with Bill Clinton on the QT. (The Gazette)
Israeli company helps you live the digital life on the QT (The Times of Israel)
“It was his idea to keep it on the QT, which is really brilliant,” Pop says now. (The Los Angeles Times)
An estimated 1.1 million Britons own a second home in the EU alone – France, Spain, Portugal and Italy, in the main – and a recent poll by survey company OnePulse revealed that around a third of them keep it on the QT. (The Telegraph)
Players may have been complaining on the QT, but now, Nightengale points out, they have their fall guy and it isn’t Reinsdorf, Ventura or Hahn. (The Washington Post)
And so, somewhat through attrition, the 90-something Sindler became a keeper of Vegas Past, holder of the neon flame, teller of tales both verifiable and strictly on the Q.T. and just between you and me. (The Las Vegas Review-Journal)