The most common and most likely answer to this crossword clue is the 7 letter word SIMPLER
I've seen this crossword clue in The Sunday Telegraph
S
I
M
P
L
E
R
Buddy explains!

The straight part
We know that "being less intelligent" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case being less intelligent = simpler.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 SIMPLER mean?
SIMPLER adjective- Uncomplicated; taken by itself, with nothing added.
- Without ornamentation; plain.
- Free from duplicity; guileless, innocent, straightforward.
- Undistinguished in social condition; of no special rank.
- Trivial; insignificant.
- Feeble-minded; foolish.
- (heading) Structurally uncomplicated.
- Mere; not other than; being only.
- One who grows or gathers simples (medicinal herbs).