The most common and most likely answer to this crossword clue is the 6 letter word VESTED
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The straight part
We know that "A particular kind of interest/in one’s underwear?" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case a particular kind of interest/in one’s underwear? = vested.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 VESTED mean?
VESTED verb- To clothe with, or as with, a vestment, or garment; to dress; to robe; to cover, surround, or encompass closely.
- To clothe with authority, power, etc.; to put in possession; to invest; to furnish; to endow; followed by with and the thing conferred.
- To place or give into the possession or discretion of some person or authority; to commit to another; with in before the possessor.
- To invest; to put.
- To clothe with possession; also, to give a person an immediate fixed right of present or future enjoyment of.
- (of an inheritance or a trust fund) To devolve upon the person currently entitled when a prior interest has ended.
- (financial) To become vested, to become permanent.
- Settled, fixed or absolute, with no contingencies.
- Dressed or clothed, especially in vestments.