AN LTT ACR FGT CREW FLEW AT NIGHT WITH AN IFR FLT PLAN WITH ONLY 1 NAV RECEIVER.

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IT WAS FOUND; DURING THE TAXI CHKLIST; THAT THE #2 NAV RADIO WAS INOP (HSI). WE THEN CONSULTED THE MEL FOR THE ACFT AND BOTH MYSELF AND MY COPLT AGREED THAT; BASED ON THE WORDING OF THE MEL; THE ACFT WAS AIRWORTHY TO FLY PART 135; IFR. THE #2 NAV RADIO WAS WRITTEN UP IN THE DR'S BY THE COPLT. DURING THE COURSE OF OUR SHIFT; OTHER PLTS WITHIN THE COMPANY WERE QUERIED AS TO THE INTERP OF THE MEL. ALL THOUGHT THE WORDING OF THE MEL WAS AMBIGUOUS. THE MAINT DEPT DECIDED TO REPAIR THE RADIO BEFORE ANY FURTHER PART 135 IFR FLTS COULD OCCUR. I FEEL THAT THE WORDING OF THE MEL; WHICH I'VE INCLUDED; CONTRIBUTED GREATLY TO THIS MISUNDERSTANDING. THE MEL SHOULD BE MORE SPECIFIC. IT SHOULD NOT BE NECESSARY FOR A FLC TO DISCUSS SEMANTICS AT THE END OF A RWY; IN THE MIDDLE OF THE NIGHT; IN IMC. A PANEL OF ATP'S; TYPED IN THE ACFT; IN THE COMFORT OF A PLT'S LOUNGE COULD NOT AGREE ON AN INTERP. WE ALL BELIEVED; HOWEVER; THAT IF THE MEL SPECIFICALLY STATED '2 VOR RECEIVERS ARE REQUIRED FOR IFR PART 135' NO PROB LIKE THIS WOULD OCCUR. MEL; REVISION #10; PAGE 34-1; SYSTEM AND SEQUENCE NUMBERS: -4A VOR RECEIVERS; REMARKS OR EXCEPTIONS: ONE MAY BE INOP FOR: PART 135 -- ONE REQUIRED FOR VFR OR VFR OVER-THE- TOP. NONE REQUIRED FOR OPS NAVIGATED BY PILOTAGE. PART 91 -- ONE REQUIRED FOR IFR. NONE REQUIRED FOR VFR.