Formal letters (8)
I believe the answer is:
epistles
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">formal letters</span>' is the definition.<br/ ><span class="explanation-format__explanation">(I've seen this in another clue)</span><br/ ><br/ >This is all the clue.<br/ ></span>
(Other definitions for epistles that I've seen before include "It sleeps among letters of the Apostles" , "Letters, missives" , "Long communications" , "Biblical letters" .)