A CRJ200 CREW ON THE CVG BLUEGRASSS 7 DEP WAS CLRED TO DOUNS BUT HEADED TO DOWNS ON V4. SIMILAR SOUNDING FIXES WITH DIFFERENT SPELLINGS CAUSED CONFUSION.

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TAKING OFF RWY 18L AT CVG; TWR ASSIGNED US A HDG OF 210 DEGS AFTER DEP. WE WERE ORIGINALLY GIVEN THE BLUEGRASS 7 DEP. AFTER A COUPLE OF MINUTES; TWR HANDED US OFF TO CGV DEP CTL. THEY TOLD US TO FLY; 'DIRECT TO DOWNS INTXN AND THE BLUEGRASS 7.' WE HAD ORIGINALLY BEEN GIVEN THE IIU TRANSITION PRIOR TO BEING GIVEN THE 210 DEG HDG BY TWR. WE DID NOT FIND DOWNS INTXN ON THE BLUEGRASS 7 IIU TRANSITION. WE DID FIND DOWNS ON V4 BETWEEN IIU AND PXV. WE BOTH ASSUMED THIS WAS THE INTXN THEY WERE TALKING ABOUT SINCE IT WAS ON OUR RTE. AFTER A COUPLE OF MINUTES; DEP ASKED IF WE WERE FLYING DIRECT TO DOWNS. WE TOLD THEM YES; BUT THEY SHOWED US FLYING OFF COURSE. WE TOLD THEM WE WERE FLYING TO DOWNS INTXN ON V4 AS PREVIOUSLY ASSIGNED. DEP RESPONDED BY SAYING THAT THEY HAD MEANT DOUNS INTXN ON THE BLUEGRASS 7; NOT DOWNS ON V4. DOUNS WAS NEVER PART OF OUR FLT PLAN. IIU WAS THE TRANSITION. TRFWA WAS THE TRANSITION FOR DOUNS; BUT IT DOESN'T GO ANYWHERE AFTER THAT; AND WAS ALSO NOT PART OF OUR FLT PLAN. AFTER STRAIGHTENING OUT THE MISUNDERSTANDING WITH THE CTLR; THEY CLRED US DIRECT TO IIU AS FILED. IN CONCLUSION; I THINK ONE OF THE INTXN NAMES SHOULD BE CHANGED BECAUSE THEY SOUND AND READ ALMOST IDENTICAL AND THEY ARE TOO CLOSE TOGETHER IN AIRSPACE SYSTEM.