The most common and most likely answer to this crossword clue is the 7 letter word ORPHREY
I've seen this crossword clue in The Times
O
R
P
H
R
E
Y
Buddy explains!
The straight part
We know that "Rich border" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case rich border = orphrey.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 ORPHREY mean?
ORPHREY noun- Any elaborate embroidery, especially when made of gold thread; an object (such as clothing or fabric) adorned with such embroidery.
- An embroidered ornamental band or border on an ecclesiastical vestment, altar frontal, etc.