The most common and most likely answer to this crossword clue is the 8 letter word BLOOMERS
I've seen this crossword clue in Financial Times
B
L
O
O
M
E
R
S
More clues leading to the result BLOOMERS
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 = bloomers.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 BLOOMERS mean?
BLOOMERS noun- An ironworker.
- A minor or embarrassing mistake with minimal results.
- A circular loaf of white bread.
- A blooming flower.
- One who blooms, matures, or develops.
- A costume for women, consisting of a short dress with loose trousers gathered around the ankles, and often a broad-brimmed hat.
- A woman who wears a Bloomer costume.
- Any of several forms of women’s divided garment for the lower body
- Women’s underpants with short legs; knickers or drawers