The most common and most likely answer to this crossword clue is the 7 letter word AMATEUR
I've seen this crossword clue in The Guardian
A
M
A
T
E
U
R
More clues leading to the result AMATEUR
- A chess defeat: game over for dilettante
- Chum in a biblical city who does something for nothing?
- Inept friend involved in gold rush initially
- A worker's assistant utterly rubbish for starters, he won't get paid
- A mature eccentric, doing it for love?
- Dabbler, pal, invested in gold rings, initially
- A surprisingly mature ham
- American friend, turning over sport, getting armchair
- A lot of the ambience around colleague comes from ham
- Partner captivated by distinctive character, not a dilettante
Buddy explains!

The straight part
We know that "armchair" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case armchair = amateur.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 AMATEUR mean?
AMATEUR noun- A lover of something.
- A person attached to a particular pursuit, study, or science as to music or painting; especially one who cultivates any study or art, from taste or attachment, without pursuing it professionally.
- Someone who is unqualified or insufficiently skillful.
- Non-professional.
- Created, done, or populated by amateurs or non-professionals.
- Showing a lack of professionalism, experience or talent.