Cryptic crossword clue
Husband, slightly impolite, heading off for convention 8

The most common and most likely answer to this crossword clue is the 8 letter word HABITUDE

I've seen this crossword clue in Financial Times
H
A
B
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Buddy explains!

The straight part
We know that "convention" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case convention = habitude.
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 HABITUDE mean?

HABITUDE noun
  1. The essential character of one's being or existence; native or normal constitution; mental or moral constitution; bodily condition; native temperament.
  2. Habitual disposition; normal or characteristic mode of behaviour, whether from habit or from nature
  3. Behaviour or manner of existence in relation to something else; relation; respect.
  4. In full habitude: fully, wholly, entirely; in all respects.
  5. Habitual association; familiar relation; acquaintance; familiarity; intimacy; association; intercourse.
  6. An associate; an acquaintance; someone with whom one is familiar.
  7. Habit; custom; usage.
  8. A chemical term used in the plural to denote the various ways in which one substance reacts with another; chemical reaction.

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