The most common and most likely answer to this crossword clue is the 8 letter word HANDLING
I've seen this crossword clue in The Daily Telegraph
H
A
N
D
L
I
N
G
Buddy explains!
The straight part
We know that "treatment" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case treatment = handling.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 HANDLING mean?
HANDLING noun- A touching, controlling, managing, using, take care of, etc., with the hand or hands, or as with the hands.
- The mode of using the pencil or brush; style of touch.
- A criminal offence, the trade in stolen goods.
- To touch; to feel or hold with the hand(s).
- To accustom to the hand; to take care of with the hands.
- To manage, use, or wield with the hands.
- To manage, control, or direct.
- To treat, to deal with (in a specified way).
- To deal with (a subject, argument, topic, or theme) in speaking, in writing, or in art.
- To receive and transfer; to have pass through one's hands; hence, to buy and sell.
- To be concerned with; to be an expert in.
- To put up with; to endure (and continue to function).
- To use the hands.
- To illegally touch the ball with the hand or arm; to commit handball.
- To behave in a particular way when handled (managed, controlled, directed).