US Supreme Court Justice Clarence Thomas was out sick Monday as the nation’s highest court opened its new term after a three-month break.

Before the court heard its first arguments of the day, Chief Justice John Roberts said Thomas, 71, was “indisposed” because of illness but would still participate in deciding the cases brought Monday.

Thomas, the longest-serving justice and the bench’s foremost conservative, likely has the flu, a court spokeswoman said.

Justice Ruth Bader Ginsburg, 86, who recently underwent cancer treatment in New York, vigorously kicked off questioning in Monday’s first case, Kahler v. Kansas, which deals with whether states can eliminate the insanity defense for criminal defendants.

The conservative-majority court also heard arguments on whether the US Constitution requires unanimous jury verdicts and on fees in patent litigation.

The bench will wrestle Tuesday with a major case on whether a landmark federal anti-discrimination law barring sex discrimination in the work place protects gay and transgender employees.

With Post Wires