What does Boxing Day have to do with boxing?
West African nation, literally "lion mountains," from Spanish sierra "mountain range" (see sierra) + leon "lion" (see lion). Attested from mid-15c. in Portuguese explorers' accounts, and a very early explanation of the name derives it from the "roaring" of thunder in the mountains. Related: Sierra Leonean.
Note: After the American Revolutionary War, attempts were made to settle freed slaves in Sierra Leone. Formerly a British protectorate, Sierra Leone became independent in 1961.