The most common and most likely answer to this crossword clue is the 6 letter word SHEIKH
I've seen this crossword clue in The Daily Telegraph
S
H
E
I
K
H
More clues leading to the result SHEIKH
- Arab chiefâs tremor when speaking
- Rock and roll heard from Muslim leader
- Ruler is upset, we hear
- Chief sound of rattle
- Leader in rock broadcast
- Flourish, we hear, as leader of Arabs
- Believer may accept his eminence as Arab leader
- Betray nervousness on the phone to Arab leader
- Saudi chief sounds like a frappe.
- In speech, rattle Arab leader
Buddy explains!

The straight part
We know that "Leader" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case leader = sheikh.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 SHEIKH mean?
SHEIKH noun- The leader of an Arab village, family or small tribe.
- An Islamic religious cleric; the leader of an Islamic religious order.
- (some Arab Gulf countries) An official title for members of the royal family as well as some prominent families.
- (1920s) A romantic lover. (from the 1921 film The Sheik)
- An Arab, especially one dressed in traditional clothing.
- An honorific for specialists in spirituality.