Well, close, but not quite perfect.
Internally the 8088 and 8086 are exactly the same. Same registers, same capabilities, etc. Registers are either 8 or 16 bit depending upon how you look at them.
When connecting to the rest of the system the 8086 is a much better processor. The 8088 connects to the rest of the machine using an 8 bit bus while the 8086 connects to the rest of the machine using a 16 bit bus. The 16 bit bus of course provides 2x the throughput to memory, if the memory is on that bus. The 8086 also has a 6 byte instruction prefetch buffer instead of the 4 byte instruction prefetch buffer that the 8088 has, which makes it slightly faster.
The 16 bit bus requires a much different motherboard though, one that looks more like an AT. PC cards designed for the original PC are only 8 bit cards, and except for the memory on the motherboard memory is added using those 8 bit cards. On a motherboard designed for an 8086 to get the best performance you need two buses - a 16 bit bus for memory and an 8 bit bus for regular PC cards. Adding memory on the 8 bit bus would be slower, or perhaps not work at all.
The 8088 allowed for less expensive motherboards and cards, while giving up some performance. The PC AT design went to a full 16 bits, both in the processor and on the bus.
Twinhead - your English is fine. Your handle is the same as a that of a well regarded Taiwanese manufacturer from the early 90s - was that your inspiration?