on the PC platform it's tended to be

byte = 8 bits

word = 16 bits

double word = 32 bits

quad word = 64 bits

but on most other systems, a "word" is merely the native width of the data bus (as opposed to the address bus)

arguably, a "word" on the 8088 was 8 bits.

any chunk of data that would fit in the accumulator register of a CPU would be considered the "word" for a particular ISA.

but then "word" got locked in a bit, and the same with C types

try writing a C compiler where a "short int" isn't 16 bits wide, i.e. a i386/x86 word...