The most common and most likely answer to this crossword clue is the 7 plus 2 plus 3 plus 3 letter word REMAINS OF THE DAY
I've seen this crossword clue in Financial Times
R
E
M
A
I
N
S
O
F
T
H
E
D
A
Y
Buddy explains!
The cryptic/wordplay part
In cryptic crossword there's often an wordplay/cryptic part as well.This part involves a more complex hint, such as an anagram, homophone, hidden word, etc.
Sadly, We don't have an explanation for this specific crossword clue yet.