The most common and most likely answer to this crossword clue is the 10 letter word EXPEDITION
I've seen this crossword clue in The Daily Telegraph
E
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Buddy explains!
The straight part
We know that "Journey/speed" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case journey/speed = expedition.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 EXPEDITION mean?
EXPEDITION noun- The act of expediting something; prompt execution.
- A military journey; an enterprise against some enemy or into enemy territory.
- The quality of being expedite; speed, quickness.
- An important or long journey, for example a march or a voyage
- A trip, especially a long one, made by a person or a group of people for a specific purpose
- The group of people making such excursion.
- To take part in a trip or expedition; to travel.