The most common and most likely answer to this crossword clue is the 4 plus 4 letter word ROAD SIGN
I've seen this crossword clue in The Guardian
R
O
A
D
S
I
G
N
More clues leading to the result ROAD SIGN
- An indication required by the way, as no grid to work with
- Staff touring area wrong to limit good advice to motorists
- Dragon is ridiculously slow, for one
- Instruction for drivers along the way
- Dragon is flying around fallen rocks?
- Notice for travellers at sea: boarding’s not starting
- It’s an indication for drivers, by the way
Buddy explains!
The straight part
We know that "slow, for one" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case slow, for one = road sign.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.