The most common and most likely answer to this crossword clue is the 7 letter word PORTION
I've seen this crossword clue in The Daily Telegraph
P
O
R
T
I
O
N
More clues leading to the result PORTION
- Tonic’s taken in the right quantity
- Part of Poins penned by playwright after a drop of porter
- Runs into medicine, which is helping
- Share
- Helping Shakespearean heroine cut down working
- Left one on allotment
- Helping put radish top into mixture
- Left on ship with one working part
- Serving last of lager in brew
- Part and at embarkation point I get aboard
Buddy explains!

The straight part
We know that "Serving" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case serving = portion.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 PORTION mean?
PORTION noun- An allocated amount.
- That which is divided off or separated, as a part from a whole; a separated part of anything.
- One's fate; lot.
- The part of an estate given or falling to a child or heir; an inheritance.
- A wife's fortune; a dowry.
- To divide into amounts, as for allocation to specific purposes.
- To endow with a portion or inheritance.