The most common and most likely answer to this crossword clue is the 7 letter word PANTIES
I've seen this crossword clue in The Sunday Telegraph
P
A
N
T
I
E
S
More clues leading to the result PANTIES
Buddy explains!

The straight part
We know that "underwear" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case underwear = panties.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 PANTIES mean?
PANTIES noun- Underpants for women and girls.
- (in the plural) Short trousers for men, or more usually boys.
- (usually in the plural, or in compounds) An article of clothing worn as underpants by women.
- A helmet cover.