The most common and most likely answer to this crossword clue is the 9 letter word ANALGESIC
I've seen this crossword clue in The Guardian
A
N
A
L
G
E
S
I
C
More clues leading to the result ANALGESIC
- Released a single, plugging covers of acoustic number
- A sign Alec's tinkered with opiate maybe
- Medication sorted out Gail’s acne
- It brings relief at one’s rear, say, turning over
- Obsessive is, say, back on drug – this one?
- Sealing cracks in air-conditioning, result is soothing
- A number of battered slices again is missing
- Lasagne’s gone off, I see — get some medicine
- Bill without a single wrong number
- A gin Alec’s drunk as a painkiller
Buddy explains!

The straight part
We know that "A number" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case a number = analgesic.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 ANALGESIC mean?
ANALGESIC noun- Any medicine, such as aspirin, that reduces pain, especially without inducing a loss of other sensation. (Contrast anesthetic.)
- (pharmaceutical effect) Of or relating to analgesia; anodyne.