The most common and most likely answer to this crossword clue is the 2 plus 3 letter word AD HOC
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More clues leading to the result AD HOC
- Casual notice — wine in short supply
- A medic going round hospital when necessary
- Hours sunk into soaring piece of music that's improvised
- Also have wine, as discussed, when needed
- Bill gets endless German wine for this purpose only
- A medic coming round hospital when required
- A medic goes round hospital unplanned
- For this particular purpose, include white wine, it’s said
- A medical professional contracted to cover hospital for a specific purpose
- Unplanned commercial wine broadcast
Buddy explains!

The straight part
We know that "for a special purpose" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case for a special purpose = ad hoc.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.