Arachnoid and Arthropod

Arachnoid noun - Air-breathing arthropods characterized by simple eyes and four pairs of legs.

Arthropod and arachnoid are semantically related. In some cases you can use "Arthropod" instead a noun "Arachnoid".

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

Arachnoid and arthropod are semantically related. Sometimes you can replace term "Arachnoid" with "Arthropod", this nouns are similar.