We are given 4 distinct letters: R, A, N, D. We need to find how many distinct 4-letter words can be formed without repeating any letter. This is a permutation of 4 unique letters: $4! = 4 \times 3 \times 2 \times 1 = 24$. Each arrangement is considered a unique word, even if it doesn’t have meaning in English. Thus, the correct answer is:
\[
{24}
\]