In modern computer science, a word generally refers to the number of bits a particular type of hardware is most comfortable performing operations on. This is almost always the same as the width of the CPU's integer and address registers, so 32-bit processors like the Pentium and the G4 have 32-bit words and the 64-bit Itanium and UltraSPARC have 64-bit words. The AltiVec-enhanced G4 has 32-bit words despite the fact that it has some 128-bit registers and can perform some special operations 128 bits at a time, since the majority of the processor is still 32-bit.
Thus, a C compiler will usually allocate a word of memory for each int.
To apply this usage historically, an example that bends the rule would be the Z80. The Z80 is an 8-bit processor with 8-bit words, even though it had some 16-bit registers (each made up of two 8-bit registers) and could do 16-bit arithmatic: it was much faster doing 8-bit operations.