The most common and most likely answer to this crossword clue is the 6 letter word OTIOSE
I've seen this crossword clue in Independent
O
T
I
O
S
E
More clues leading to the result OTIOSE
- Redundant seaman severs old hawser
- Extracting power from unstable isotope is superfluous
- Nothing to elicit, I shut up, being indolent
- Note, very big, in Old English serving no purpose
- Futile notions to sacrifice two knights before end of game
- Ten toes spread out with no purpose
- Useless series of books that’s about a sailor
- Oddly padded, it could be fortuitous yet uncalled-for
- Playing footsie with standoffish female? That’s futile
- …useless and disorienting too I see, taking it
Buddy explains!

The straight part
We know that "superfluous" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case superfluous = otiose.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 OTIOSE mean?
OTIOSE adjective- Having no effect.
- Done in a careless or perfunctory manner.
- Reluctant to work or to exert oneself.
- Of a person, possessing a bored indolence.
- Having no reason for being (raison d’être); having no point, reason, or purpose.