I don't know, but 'swap' seems to have become the standard term for the operation, used in places like the C bswap family of functions and the x86 'bswap' instr

I don't know, but 'swap' seems to have become the standard term for the operation, used in places like the C bswap family of functions and the x86 'bswap' instruction. My (totally unsupported and unresearched) guess is that it became popular as a term when 16-bit architectures were common -- "swap the bytes in a 16 bit value" is unambiguous. The Arm architecture does call this operation "reverse bytes", though, so it's not universal to call it "swap".