addl, subl, movl all assume the operands are size 4 bytes. This size is referred to by IA32 as long and is also called double word.

So a word in IA32 terminology means 2 bytes.

There are 5 mov.. instructions:

  movl S,D    move double word (4 byte operands)
  movw S,D    move word  (2 byte operands)
  movb S,D    move byte (1 byte operands)

  movsbl S,D  move Source byte to a double word Destination using sign
              extension 

  movzbl S,D  move Source byte to a double word Destination 0-extended