The most common and most likely answer to this crossword clue is the 6 letter word LINENS
I've seen this crossword clue in Independent
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More clues leading to the result LINENS
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The straight part
We know that "undergarments" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case undergarments = linens.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 LINENS mean?
LINENS noun- Thread or cloth made from flax fiber.
- Domestic textiles, such as tablecloths, bedding, towels, underclothes, etc., that are made of linen or linen-like fabrics of cotton or other fibers; linens.
- A light beige colour, like that of linen cloth undyed.
- Household textiles made of linen-like cloth (such as cotton fabric), including tablecloths and bed sheets. The singular, linen, of this sense is rare.
- Undergarments, underwear.