A TAXIING B747-400 CROSSES RWY 4L WITHOUT CLRNC FROM GND CTLR AT ORD; IL.

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THE INITIAL TAXI INSTRUCTIONS FROM GATE AREA FROM ORD FROM GND CTL WERE TO 'TAXI TO RWY 4L; L TURN ON TXWYS B; J; AND W.' ONCE ON TXWY H WITH OUR ACFT HDG 270 DEGS AND APCHING THE AREA OF TXWYS A AND B; GND SAID 'THE ACFT ON TXWY R WILL GIVE WAY TO YOU.' I TOLD THE CAPT THAT I WOULD BE OFF THE RADIO GETTING THE PAX COUNT AND WTS FOR TKOF. WHILE I WAS OFF THE RADIO; I COULD TELL THE CAPT AND THE GND CTLR WERE TALKING. WE THEN CONTINUED STRAIGHT AHEAD ON TXWY H AND CROSSED RWY 4L. THERE WAS NO TFC ON THE RWY OR THE APCH OR RWY 4L RUNUP AREA. AFTER XING RWY 2L; ON TXWY H; I RETURNED TO MONITOR THE GND FREQ WHERE THE CAPT AND THE GND CTLR WERE DISCUSSING THE TAXI RTE. GND ASKED WHAT WE WERE DOING. THE CAPT SAID WE WERE 'TAXIING STRAIGHT AHEAD TO RWY 4L PER YOUR LAST INSTRUCTIONS.' SINCE THIS WAS DIFFERENT THAN OUR ORIGINAL CLRNC TO TAXI; I ASSUMED THAT WHILE I WAS OFF THE RADIO THAT THE GND CTLR HAD CHANGED OUR TAXI RTE AND THAT THE CAPT WAS COMPLYING WITH HIS INSTRUCTIONS. WHEN I ASKED WHAT WAS GOING ON; THE CAPT EXPLAINED THAT HE WAS FOLLOWING GND INSTRUCTIONS TO TAXI STRAIGHT AHEAD; AND THAT THE ACFT ON TXWY R FACING SE WOULD BE HOLDING FOR US. THE CAPT TAXIED DOWN TXWY H; MADE A L TURN ON TXWY J AND A L TURN ON TXWY W; HOLDING SHORT OF RWY 4L. CONTRIBUTING FACTORS: AN ENG PROB CAUSED US TO RETURN TO THE GATE FOR MAINT. UPON OUR TAXI OUT; THE CHIEF PURSER TOLD THE CAPT SOME OF THE PAX HAD DEPLANED; BUT DID NOT GIVE US A COUNT. THIS CAUSED US TO ISOLATE THE RADIOS; CALL FOR A COUNT; ADVISE LOAD CTL OF THE CHANGE. A SHORT TAXI; WITH POOR ATC LANGUAGE 'TAXI STRAIGHT AHEAD' WHEN A 45 DEG TURN WAS REQUIRED TO GET TO TXWY B FROM TXWY H; WAS ALSO CONFUSING. LANGUAGE SUCH AS 'CONTINUE TAXI TO RWY 4L AS CLRED' OR 'CONTINUE; L ON TXWY G; R ON TXWY J; R ON TXWY W' WOULD HAVE ELIMINATED ANY CONFUSION ON THE PART OF THE CAPT. A PROC TO ISOLATE THE RADIOS FOR CABIN COM AND LOAD CTL COULD BE PUT IN PLACE TO ONLY DO THIS WHILE THE ACFT IS STOPPED. BUT THIS IS NOT PRACTICAL. BETTER ATC ADHERENCE TO STANDARD PHRASEOLOGY AS WELL AS REPEATING FULL CLRNCS WHEN THE INITIAL CLRNCS HAVE CHANGES IN PARTS OF THE INITIAL CLRNC.