The most common and most likely answer to this crossword clue is the 8 letter word CEREBRAL
I've seen this crossword clue in The Guardian
C
E
R
E
B
R
A
L
More clues leading to the result CEREBRAL
- Intellectual having half of bran in oats, say
- British tucking into breakfast food of an intellectual cast
- Brainy brother drinking rye? The opposite
- Brainy Anglican relative wins cups
- Intelligent British farmer finally feeding agricultural crop
- Perhaps rye drinking leads to blindness and rotting of the brain
- Intellectual brother tucking into cornflakes, perhaps
- Intellectual’s brother tucks into rye, say
- Half serving of bran added to grain of loaf
- Intellectual brother tucked into breakfast food
Buddy explains!

The straight part
We know that "Intellectual" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case intellectual = cerebral.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 CEREBRAL mean?
CEREBRAL adjective- Of, or relating to the brain, cerebrum, or cerebral cortex.
- Intellectual rather than emotional.
- Retroflex.