The most common and most likely answer to this crossword clue is the 0 letter word
I've seen this crossword clue in Independent
More clues leading to the result ADULT
- Grown-up daughter wearing gold locket that's empty
- A mostly uninteresting time for grown-up
- Hand out lots now and again, but not for children
- See 3 Down
- Mature blue
- Responsible individual said, “every second counts”
- A fool drops love for university, getting mature
- A largely sombre time for a grown-up
- Figure that’s beyond a minority?
- Responsible person gives notice last month
Buddy explains!
The straight part
We know that "see 3D" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case see 3d = adult.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.