Arthropod and Millipede

Arthropod noun - Invertebrate having jointed limbs and a segmented body with an exoskeleton made of chitin.

Millipede and arthropod are semantically related. In some cases you can replace term "Millipede" with "Arthropod", this nouns are similar.

Millipede noun - Any of numerous herbivorous nonpoisonous arthropods having a cylindrical body of 20 to 100 or more segments most with two pairs of legs.

Arthropod and millipede are semantically related. You can use "Arthropod" instead a noun "Millipede".