The most common and most likely answer to this crossword clue is the 4 letter word AIDE
I've seen this crossword clue in The Guardian
A
I
D
E
More clues leading to the result AIDE
- Answer promoted in plan to desert assistant
- Assistant thought the last to become leader
- One helping girl to avoid extremes
- Officer in A & E the writer would flee?
- Notion back to front for political supporter
- Sidekick's scheme's last to start
- A fish makes one helping
- Military PA in reserve, missing start of service leave
- Unveiled female personal assistant
- A swimmer’s assistant
Buddy explains!

The straight part
We know that "assistant" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case assistant = aide.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 AIDE mean?
AIDE noun- An assistant.
- An officer who acts as assistant to a more senior one; an aide-de-camp.