The most common and most likely answer to this crossword clue is the 12 letter word PERAMBULATOR
I've seen this crossword clue in Financial Times
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More clues leading to the result PERAMBULATOR
Buddy explains!
The straight part
We know that "Carriage reserved for small charge" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case carriage reserved for small charge = perambulator.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 PERAMBULATOR mean?
PERAMBULATOR noun- A baby carriage; a pram.
- One who perambulates.
- A surveyor's instrument for measuring distances, consisting of a wheel that rolls over the ground, along with a clockwork apparatus and a dial plate upon which the distance travelled is shown by an index.