BIZJET CREW TOOK OFF WITHOUT CLRNC.

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WE TAXIED FOR DEP AFTER RECEIVING OUR IFR CLRNC. AS THE SIC (PNF) ON THIS LEG; I GAVE THE CHKLIST CHALLENGES AND THE CAPT (PF) GAVE THE APPROPRIATE RESPONSES. WE COMPLETED THE BEFORE TKOF CHKLIST AS WE APCHED THE RWY THRESHOLD. HOLDING SHORT OF THE RWY; THE CAPT ASKED ME TO ADVISE THE TWR WE WERE READY FOR TKOF. HE MADE A CABIN CALL TO TELL OUR PAX TO CHK THEIR SEATBELTS AND I TOLD THE TWR WE WERE READY FOR DEP. VERIFYING DEP FREQ AND XPONDER CODE FROM OUR FLT LOG; I ACKNOWLEDGED THE TWR'S CLRNC BY READING IT BACK. THINKING WE HAD RECEIVED OUR TKOF CLRNC; I TOLD THE CAPT WE WERE READY FOR TKOF. AT THIS TIME THERE WAS ALSO SOME DISTURBANCE BEHIND US; AS ONE OF THE PAX WAS OUT OF HIS SEAT AND THE CAPT DIVERTED HIS ATTN TO ASK HIM TO BE SEATED AS WE WERE READY FOR TKOF. LINING UP ON THE RWY WE COMPLETED OUR LINE-UP CHKS AND I TOLD THE CAPT I WAS READY. THE CAPT ADVANCED THE PWR AND I BEGAN TO MONITOR THE INSTS TO MAKE THE CALLOUTS. WE WERE ACCELERATING RAPIDLY WHEN THE TWR CALLED US '...YOU ARE NOT CLRED FOR TKOF; ABORT YOUR TKOF!' AT THIS POINT IN THE TKOF FROM THIS HIGH ALT ARPT; IT APPEARED UNSAFE TO ATTEMPT A HIGH SPD ABORT. THE CAPT VISUALLY CLRED THE RWY AHEAD AND THE DEP PATH AND SAID WE NEEDED TO CONFIGURE; WHICH I BELIEVE UNDER THE CIRCUMSTANCES WAS THE SAFER ACTION. THE TWR THEN SAID '...CANCEL YOUR TKOF CLRNC' AT WHICH TIME WE WERE ROTATING FOR LIFTOFF. AS WE WERE CLBING OUT; WE REFOCUSED OUR ATTN ON FLYING THE AIRPLANE AND CONTINUING WITH THE AFTER TKOF/CLB PROCS. THE TWR ASKED IF WE COULD HEAR THEM AND I RESPONDED I COULD NOW HEAR THEIR CALLS. THEY ADVISED US OF A PREVIOUSLY DEPARTED C421 ON IFR DEP 5 MI TO THE N AND CLBING OUT OF 10500 FT. TO AVOID A TFC CONFLICT; WE MAINTAINED A 340 DEG HDG AND REQUESTED A VFR CLB TO 16000 FT. THE TWR CLRED US FOR A VFR CLB AND TOLD US TO CALL DEP CTL. WE AVOIDED THE ADVISED TFC WITH REF TO OUR TCASII AND VISUALLY LOOKING FOR THE ACFT. THERE WAS NO TCASII ALERT OR EVASIVE ACTION REQUIRED. LATER WE CALLED THE TWR. THEY SAID THEY HAD REVIEWED THE TAPES AND HAD CLRED US 'INTO POS AND HOLD;' WHICH THEY SAID I HAD READ BACK. NEXT THEY HAD ADVISED US THAT THERE WOULD BE A COUPLE MIN HOLD DUE TO DEPARTED IFR TFC. I HAD NOT RESPONDED TO (NOR DO I REMEMBER HEARING) THIS XMISSION. AS THE TWR SAID THE TAPES REVEALED I HAD READ BACK THEIR CLRNC; I OBVIOUSLY MISSED THE INTENT OF THEIR CLRNC; EVEN THOUGH I READ IT BACK. CONTRIBUTING FACTORS INCLUDED A FEELING OF BEING RUSHED TO COMPLETE THE CHKLIST ITEMS AND VERIFY THE FREQS AND CODES WERE SET IN FOR TKOF; THE ADDED CONFUSION OF A PAX NOT BEING SEATED AND A POSSIBLE MIKE BEING INADVERTENTLY ACTIVATED WHEN THE TWR WAS TRYING TO COM THE DELAY MESSAGE. THIS WAS A VERY SERIOUS ERROR AND CAUSES ME TO AGAIN NOT ALLOW WHAT IS HAPPENING TO MAKE US RUSH AND NOT CAREFULLY VERIFY OUR CLRNCS. I BELIEVE THE CAPT'S CONTINUING THE DEP WAS THE SAFE CHOICE WHEN A REJECTED TKOF UNDER THIS SIT MAY HAVE LED TO AN OVERRUN. AFTER OVER 30 YRS OF PROFESSIONAL FLYING; I REALIZE THAT I CAN STILL MAKE MISTAKES AND I MUST CONTINUE TO EXERCISE CARE.