Slow arrangement for Elton after horrible din (8)
'slow' is the definition.
'arrangement for elton after horrible din' is the wordplay.
'arrangement for' indicates an anagram (I've seen this in other clues).
'after' means one lot of letters go next to another.
'horrible' is an anagram indicator.
'elton' with letters rearranged gives 'olent'.
'din' anagrammed gives 'ind'.
'olent' after 'ind' is 'INDOLENT'.
(Other definitions for indolent that I've seen before include "Disinclined to exert oneself", "not willing to work", "Work-shy", "Lethargic", "Disinclined to exertion or work".)