The most common and most likely answer to this crossword clue is the 4 letter word MEMO
I've seen this crossword clue in The Guardian
M
E
M
O
More clues leading to the result MEMO
- Person writing second message shortened by 60%
- Reminder – the writer of this puzzle takes a little time
- Third note, then second note
- Note from doctor following case of malpractice
- One state followed by another, note
- Your setter needs a second reminder
- Note clip from home movie
- Written communication from troublesome Moscow
- Note this writer being given tick
- Note backed home-made clothes
Buddy explains!

The straight part
We know that "message shortened by 60%" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case message shortened by 60% = memo.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.
What does MEMO mean?
MEMO noun- A short note; a memorandum.
- A record of partial results that can be reused later without recomputation.
- To record something; to make a note of something.
- To send someone a note about something, for the record.