The most common and most likely answer to this crossword clue is the 3 plus 6 letter word RIO GRANDE
I've seen this crossword clue in Financial Times
R
I
O
G
R
A
N
D
E
More clues leading to the result RIO GRANDE
- Answer found in ordering afresh for banker
- Film old relative during journey on horseback
- Long-distance runner, elderly Brazilian possibly died before end of race
- Old relative is breaking journey to Trump’s walled river
- Old relative to be carried across river
- Ordering a suspect into river
- One captivated by wild or garden flower
- Long river journey interrupted by old, old woman
- Ordering reconstruction around American border with Mexico
- For cultivation, ordering a New World flower
Buddy explains!
The straight part
We know that "a border river" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case a border river = rio grande.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.