The most common and most likely answer to this crossword clue is the 3 letter word EFF
I've seen this crossword clue in Financial Times
E
F
F
Buddy explains!
The straight part
We know that "Partner of blind" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case partner of blind = eff.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 EFF mean?
EFF verb- Fuck (the taboo swear word, but not in the sense "to copulate")