Concept:
Arrange the letters in alphabetical order and then find the letter farthest (last position) from the first letter.
Step 1: Write the letters of CYCLINDER.
\[
C,\ Y,\ C,\ L,\ I,\ N,\ D,\ E,\ R
\]
Step 2: Arrange alphabetically.
\[
C,\ C,\ D,\ E,\ I,\ L,\ N,\ R,\ Y
\]
Step 3: Identify positions.
First letter = C
Farthest letter (last position) = Y
Hence, the required letter is Y.