The most common and most likely answer to this crossword clue is the 8 plus 6 letter word STEPPING STONES
I've seen this crossword clue in The Times
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Buddy explains!
The straight part
We know that "River crossing" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case river crossing = stepping stones.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 STEPPING STONES mean?
STEPPING STONES noun- A stone that can be stepped on in crossing something, especially a marsh or creek.
- Something used as a way to progress to something or somewhere else.