I've searched around, and there are responses to whether a Drupal term can have multiple parents in different vocabularies, but I'm wondering if I can do it for those within the same vocabulary?
Like this:
Vocabulary Name
Parent Term 1
- Fruit
- Protein
- Candy
Parent Term 2
- Dairy
- Protein
- Vegetables
Drupal core does not support that kind of functionality so there are two way to do it.
Programmaticly. That means that you will have to hack Drupal`s core in order to do it. Here is an instruction: http://greenash.net.au/thoughts/2005/02/cross-vocabulary-taxonomy-hierarchies/
Using modules. This will only give you parent relation like relationships between terms but it is much easier to set up. Modules like Term Relations or References or Vocabulary reference should do the job