The most common and most likely answer to this crossword clue is the 5 letter word BRAIN
I've seen this crossword clue in The Times
B
R
A
I
N
More clues leading to the result BRAIN
- Bachelor artist, fashionable — bright guy
- Puzzle sane arbiter’s sorted out
- Shrewdness of British government, we hear
- Water fills empty butt, as always getting round problem
- Barrister's case isn't simplified when one's ignored problem
- Egghead having drinks with ‘er: problem!
- Be in tears about crossing a river — it’s a problem
- Mind sheikhdom deporting a husband
- Mind one tucks into fibrous food
- Refuse to accept source of intelligence and intellect
Buddy explains!

The straight part
We know that "bright guy" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case bright guy = brain.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 BRAIN mean?
BRAIN noun- The control center of the central nervous system of an animal located in the skull which is responsible for perception, cognition, attention, memory, emotion, and action.
- An intelligent person.
- (in the plural) Intellect.
- By analogy with a human brain, the part of a machine or computer that performs calculations.
- Oral sex.
- Mind.
- To dash out the brains of; to kill by smashing the skull.
- To strike (someone) on the head.
- To destroy; to put an end to.
- To conceive in the mind; to understand.