For example, in the majority of football (soccer) leagues, you'll have a number of tiers such as the first division, second division, third, etc. At the end of each season the few top teams in the second division are promoted to the first division, and the few bottom teams in the first division are relegated to the second division.
What would the second division be refered to from the first division, and visa versa?
I don't think parent/child necessarily makes sense, as this to my mind indicates some level of succession and timing, such as the parenting occuring before the child, where as in this context they are potentially conceived and occur at the same time.
To clarify I'm looking for the noun, such as:
- The first division is the parent of the second division.
- The second division is the child of the first division.