AN ACR DH8 FLEW THE FILED RTE OUT OF EAT VERSUS THE RTE GIVEN THEM BY THE ARTCC CTLR. ACFT WENT WBOUND OUT OF EAT INSTEAD OF EBOUND TO EPH AND THE EPH4 ARR.

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I WAS THE FO; PNF; ON A WENATCHEE; WA; TO SEATTLE; WA; FLT. I CALLED AND REQUESTED AN IFR CLRNC FROM WENATCHEE TO SEATTLE FROM ZSE ON 126.10. I TOLD THEM THAT WE WOULD BE DEPARTING RWY 30 FROM WENATCHEE IN 2-3 MINS. OUR FILED CLRNC TO SEATTLE AS IT'S PRINTED ON OUR DISPATCH RELEASE IS 'EAT.V120.SEA.' WHEN THE CTLR ISSUED US THE CLRNC; HE SAID THAT WE WERE CLRED TO SEATTLE VIA V120.EPH.EPH4 ARR. NOW; UNBEKNOWNST TO ME; THE CTLR WANTED US TO FLY EBOUND FOR TFC SEPARATION. WE (THE CAPT AND I) HAD NO REASON TO BELIEVE THAT WE SHOULD FLY EBOUND RATHER THAN W; LIKE OUR DISPATCH RELEASE CLRNC SPECIFIES. ACCORDING TO THE CTLR (CTR) WE DID NOT CAUSE ANY TFC CONFLICTS OR SEPARATION PROBS. HOWEVER; THE POTENTIAL WAS THERE. HAD THE CTLR PREFACED HIS ISSUED CLRNC TO US WITH THE TERMINOLOGY; 'ATC CLRS XXXX TO SEATTLE VIA REVISED ROUTING' OR 'THIS IS AN AMENDMENT TO YOUR FILED CLRNC; ATC NOW CLRS XXXX TO SEATTLE VIA....' HAD THE CTLR ALERTED US WITH THE PROPER TERMINOLOGY THIS WOULD'VE ALERTED BOTH THE CAPT AND I TO A REVISED ROUTING. HENCE; DUE TO THE IMPROPER TERMINOLOGY AND VERY SIMILAR VERBIAGE IN THE ATC CLRNC NOTHING PUT THE CAPT AND I IN A SIT TO BE WARY OF A CHANGE IN PLANS. WE DIDN'T HAVE ANY REASON TO FEEL WE WERE DOING ANYTHING WRONG BECAUSE WE WEREN'T GIVEN THE PROPER TERMINOLOGY TO ALERT US TO A REVISED CLRNC. ANYTIME SOMETHING DIFFERENT IS ISSUED TO PLTS FROM ATC; ATC MUST TELL US WHY THEY ARE GIVING US CERTAIN INSTRUCTIONS TO AVOID POTENTIAL CONFLICTS SUCH AS THIS. SUPPLEMENTAL INFO FROM ACN 414309: WE WERE GIVEN A CLRNC THAT WAS DIFFERENT FROM OUR 'CANNED' RTE. WE DIDN'T NOTICE THAT THE CLRNC WAS DIFFERENT BECAUSE THE VICTOR AIRWAY THAT WE WERE CLRED VIA WAS THE SAME AS THE AIRWAY WE WERE ORIGINALLY FILED ON V120.