The most common and most likely answer to this crossword clue is the 7 letter word SOOTHER
I've seen this crossword clue in The Times
S
O
O
T
H
E
R
More clues leading to the result SOOTHER
Buddy explains!

The straight part
We know that "Calmer" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case calmer = soother.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 SOOTHER mean?
SOOTHER adjective- True.
- Pleasing; delightful; sweet.
- One who, or that which, soothes.
- A plastic device that goes into a baby’s mouth, used to calm and quiet the baby.
- To soothe.