The most common and most likely answer to this crossword clue is the 7 letter word GLOSSAL
I've seen this crossword clue in The Times
G
L
O
S
S
A
L
Buddy explains!

The straight part
We know that "relating to tongue" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case relating to tongue = glossal.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 GLOSSAL mean?
GLOSSAL adjective- Of, or relating to the tongue.