The most common and most likely answer to this crossword clue is the 7 letter word SPEEDOS
I've seen this crossword clue in Independent
S
P
E
E
D
O
S
More clues leading to the result SPEEDOS
- Singular tinkles having function in clocks [7]
- Doss about, eating first piece of picnic in swimming trunks
- Note sea’s rising — go in wearing these
- Amphetamines and stuff that’s inside most trunks
- Son went on Big Dipper in these?
- Go in, doss about and cover balls with these, maybe
- Help to patrol rising sea which swimmers may be in
- On a dash, gauge small, tight pants
- Backed appeal for help framing main indicators of progress
Buddy explains!

The straight part
We know that "trunks" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case trunks = speedos.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 SPEEDOS mean?
SPEEDOS noun- A tight-fitting swimsuit, especially commonly worn by competitive swimmers and divers. Usually implies a brief or bikini style swimsuit.
- A speedometer, particularly one in a race car or other automobile.