Yes, taboo is a Scrabble word!

Verb

1. Declare as sacred and forbidden

Adjective

1. Excluded from use or mention

2. Forbidden to profane use especially in South Pacific islands

Noun

1. A prejudice (especially in Polynesia and other South Pacific islands) that prohibits the use or mention of something because of its sacred nature

2. An inhibition or ban resulting from social custom or emotional aversion