If you can form exactly one meaningful English word using the $1^{\text{st}}$, $5^{\text{th}}$, $6^{\text{th}}$, and $8^{\text{th}}$ letters of the word 'INFORMATION', what will be the fourth letter of that word?

Let's find the designated letters from the word INFORMATION:
* $1^{\text{st}}$ letter = $\text{I}$
* $5^{\text{th}}$ letter = $\text{R}$
* $6^{\text{th}}$ letter = $\text{M}$
* $8^{\text{th}}$ letter = $\text{T}$

The extracted letters are $\text{I, R, M, T}$.
Arranging these letters forms exactly one meaningful English word: TRIM.
The fourth letter of the word 'TRIM' is M.