What does CHAIN mean?

noun

1. a series of things depending on each other as if linked together“the chain of command”
2. (chemistry) a series of linked atoms (generally in an organic molecule)
3. a series of (usually metal) rings or links fitted into one another to make a flexible ligament
4. (business) a number of similar establishments (stores or restaurants or banks or hotels or theaters) under one ownership
5. anything that acts as a restraint
6. a unit of length
7. a series of hills or mountains“the valley was between two ranges of hills”
8. a linked or connected series of objects“a chain of daisies”