The most common and most likely answer to this crossword clue is the 6 letter word ONE-UP
I've seen this crossword clue in Financial Times
O
N
E
-
U
P
More clues leading to the result ONE-UP
Buddy explains!
The straight part
We know that "having slim advantage" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case having slim advantage = one-up.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 ONE-UP mean?
ONE-UP noun- An item that grants the player an extra life in the game, staving off game over by one more try.
- In a game with multiple players, an indicator or identifier of player 1.
- (especially in phrases like get one up on someone) An advantage over someone.
- To outdo, to do something slightly better than a competitor's prior effort.