The most common and most likely answer to this crossword clue is the 6 letter word MEMBER
I've seen this crossword clue in Financial Times
M
E
M
B
E
R
More clues leading to the result MEMBER
- One in the club, married, remains smouldering
- Parliamentarian finding honour in French waters
- Clubman recalled dropping couples outside
- One in the club to recall blackballing the first couple
- Married before the end of three months — she’s in the club
- Johnson & Johnson?
- One in a class to recall skipping RE
- Setter right to accept award – one with a sense of belonging
- Don’t forget to ditch repulsive, gutless parliamentarian
- Recall missing sappers, part of army unit?
Buddy explains!

The straight part
We know that "One in the club" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case one in the club = member.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 MEMBER mean?
MEMBER noun- One who officially belongs to a group.
- A part of a whole.
- Part of an animal capable of performing a distinct office; an organ; a limb.
- The penis.
- One of the propositions making up a syllogism.
- An element of a set.
- A function or piece of data associated with each separate instance of a class.
- The judge or adjudicator in a consumer court.
- A part of a discourse or of a period, sentence, or verse; a clause.
- Either of the two parts of an algebraic equation, connected by the equality sign.
- A file stored within an archive file.
- (obsolete outside dialectal) To remember.
- To cause to remember; to mention.