Attune Domain (3.5e Feat)
From D&D Wiki
You incorporate the workings of a divine domain into your magic.
Prerequisite: Caster level 1+. Must follow a god or philosophy consistent with the chosen domain.
Benefit: Choose a domain when this feat is selected. Every spell from that domain is considered to be on your spell-list for any spellcasting classes you happen to have. These spells are considered to be spells known at the level they appear in the chosen domain. These spells are cast (and prepared, if appropriate) as normal for your class.
Special: You may select this feat multiple times, its effects do not stack. Each time you may select a new domain, so long as your chosen god or philosophy can incorporate all of them. As usual, your DM must approve any god or philosophy. You may not have more than three attuned domains or spheres together.