Herb
The kitchen's warmest leaf, and the plant Culpeper lost his temper over.
These are associations the community holds, not settled fact — the more a reading is shared, the bolder it sits.
Basil arrived in Europe from India and picked up wildly contradictory reputations on the way. In parts of the Mediterranean it was a funeral herb and a plant of mourning; in others it was courtship, placed on a windowsill by a woman signalling that a suitor would be welcome. Its name is usually connected to the Greek for king, though a competing derivation links it to the basilisk, which tells you what kind of arguments surrounded it.
Those arguments are the fun of the plant. Renaissance authorities could not agree whether it was wholesome or poisonous, and repeated a story that basil left under a stone would breed scorpions, or that smelling it too much would breed one in the brain. Craft use today is settled and cheerful by comparison: basil for money, for love, for peace in a household, for a shop's first customer of the day.
Tulsi, or holy basil, is a related but distinct plant with a devotional role in Hinduism that is not interchangeable with the culinary sort. If a text calls for tulsi specifically, it means tulsi, and it is worth knowing whose practice you are borrowing.
Readings practitioners have offered, ordered by how many recognise them. Take what serves, leave the rest.
Carried forward
Nicholas Culpeper, The Complete Herbal (1653)
Culpeper begins: "This is the herb which all authors are together by the ears about, and rail at one another (like lawyers)." He then sets out both sides, gives basil to Mars under Scorpio, and declines to settle it — which for him is remarkable restraint.
Carried forward
Duskveil editorial note
Holy basil, tulsi, is venerated in Hindu household practice and is not a swap for the culinary plant. Where a recipe names it, the practice around it belongs to a living tradition and is worth learning properly rather than approximating.
Credit what you carry. Much of this comes from living traditions, and some of it from traditions that are closed — held by particular peoples and not offered for general use. Where you know whose practice a reading came from, name them; where you don't, say that too.