What does the number of bit of microprocessor mean?
How many bits wide its registers are: usually, its data registers (the ones which can load and store data and perform logical and arithmetical functions).

The 8086 has 16-bit data and address registers, and a 16-bit data path to external memory.

The 8088 has 16-bit data and address registers, but only an 8-bit data path to external memory. Because it is internally identical to the 8086, it is also considered to be a 16-bit processor.

The 8085 has 8-bit data registers and 16-bit address registers. The address registers (apart from SP) are made up of pairs of 8-bit data registers. The fact that it is possible to add one address register to another isn't enough to make the processor considered to be "16-bit".