The most common and most likely answer to this crossword clue is the 5 letter word VELAR
I've seen this crossword clue in The Times
V
E
L
A
R
Buddy explains!
The straight part
We know that "describing part of mouth" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case describing part of mouth = velar.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 VELAR mean?
VELAR noun- A sound articulated at the soft palate
- Articulated at the velum or soft palate.
- Referring to a veil or velum.