The most common and most likely answer to this crossword clue is the 7 letter word CONCEPT
I've seen this crossword clue in Financial Times
C
O
N
C
E
P
T
Buddy explains!
The straight part
We know that "idea" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case idea = concept.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 CONCEPT mean?
CONCEPT noun- An abstract and general idea; an abstraction.
- Understanding retained in the mind, from experience, reasoning and imagination; a generalization (generic, basic form), or abstraction (mental impression), of a particular set of instances or occurrences (specific, though different, recorded manifestations of the concept).
- In generic programming, a description of supported operations on a type, including their syntax and semantics.