AFTER TWR TOLD FLC TO HOLD SHORT OF RWY; CAPT THOUGHT THEY WERE CLRED ONTO THE RWY. FLC HAD BEEN TOLD THEY HAD 1 1/2 HR DELAY; SO ENGS WERE SHUT DOWN AND THEY WERE WAITING WHEN AFTER JUST A SHORT TIME THEY WERE TOLD TO GET READY FOR A QUICK GO. SCRAMBLING TO START ENGS; FINISH CHKLISTS; FLC EVIDENTLY BECAME TOO DISTRACTED.

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ADVISED THAT FLT DELAYED FOR 1 1/2 HRS. TOLD BY GATE AGENT TO DEPART GATE AS IT WAS NEEDED FOR AN INBOUND FLT. START AND TAXI OUT WERE UNEVENTFUL. DIRECTED BY GND CTL TO HOLD IN THE WAITING AREA SHORT OF RWY 29L. WITH ABOUT 1 HR TO GO TO PROJECTED WHEELS UP TIME; TAXIED TO APPROX ONE SHIP LENGTH SHORT OF THE HOLD LINE AT RWY 29L AND PARKED WELL TO E SIDE. THE CAPT SHUT DOWN ENGS AND ADVISED THE FLT ATTENDANTS TO BEGIN DRINK SVC AS WE STILL HAD QUITE A WHILE TO WAIT. APPROX 10 MINS LATER; TWR ADVISED US TO START UP QUICKLY AS RELEASE HAD BEEN OBTAINED. WE SCRAMBLED THROUGH START AND BEFORE TAXI CHKS. WHILE GOING THROUGH THE TKOF CHK; THE CAPT BEGAN MOVING FORWARD. THE TWR DIRECTED US TO TAXI TO HOLD LINE AND HOLD SHORT. I RESPONDED ON RADIO THAT WE WERE TO HOLD SHORT AND AFTER THE RADIO CALL AGAIN VERBALIZED INTERCOCKPIT THE WORDS 'HOLD SHORT;' AS IS MY HABIT PATTERN. I CONTINUED WITH THE TKOF CHK. WHEN I NOTICED DURING THE CHK THAT WE WERE STILL MOVING; AND IN THE VICINITY OF THE HOLD LINE; I AGAIN STATED THAT WE WERE DIRECTED TO HOLD SHORT. AFTER COMPLETING IN-COCKPIT ITEMS OF THE TKOF CHK; I RETURNED 'HEADS OUT;' NOTICED WE WERE ON THE RWY AND QUERIED THE CAPT. HE STATED HE THOUGHT WE HAD BEEN CLRED TO POS AND HOLD. A FLT ON EXTENDED FINAL CALLED THEY WERE GOING AROUND DUE TO THE ACFT ON THE RWY (US). IN REVIEW; THE CAPT HAD 4 DISTINCT VERBAL INPUTS TO 'HOLD SHORT.' HIS GESTURES/NODS INDICATED HE UNDERSTOOD THE CLRNC. TO PREVENT THIS EVENT FROM RECURRING; THE CAPT SHOULD VERBALIZE ALL KEY MOVEMENT DIRECTIVES. MOST I FLY WITH DO.