Holy basil is also known as tulsi in India. I have heard a story that Thai people moving to India are warned not to pluck the leaves from the plant without seeking permission as they are holy plants.
Holy basil is gapow in Thai. There are several varieties in Thailand. Some are grown wildly. If you trek in Thailand, check out for the reddish, purplish variety. It can be grown from seeds in the US in the summer.
You are probably familiar with 'gai pad gapow'. Frequently here in the US, when you order 'pad gapow' in a restaurant, you do not get the real gra pow, but instead sweet basil. They are not the same. However, if push comes to shove, sweet basil is better than nothing.
Gapow has a different smell and flavor than basil. Its branches and leaves are covered with tiny hair. It has a hot spicy smell. If you are making 'pad gra pow', don't sacrifice the taste, use all that you've got. It is worth it.