The most common and most likely answer to this crossword clue is the 7 letter word BROADEN
I've seen this crossword clue in The Daily Telegraph
B
R
O
A
D
E
N
More clues leading to the result BROADEN
- Open up mountain accessed by lane
- Extend route into mountain
- Make wider street to cut through Scottish mountain
- Extend thoroughfare through mountain
- Trail found in mountain stretch
- Expand passage through mountain
- Expand the street passing through Big clock
- Served up one drab spread
- Widen pass through Scottish mountain
Buddy explains!

The straight part
We know that "Widen" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case widen = broaden.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 BROADEN mean?
BROADEN verb- To make broad or broader.
- To become broad or broader.