The most common and most likely answer to this crossword clue is the 6 letter word FURROW
I've seen this crossword clue in The Guardian
F
U
R
R
O
W
Buddy explains!
The straight part
We know that "Line" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case line = furrow.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 FURROW mean?
FURROW noun- A trench cut in the soil, as when plowed in order to plant a crop.
- Any trench, channel, or groove, as in wood or metal.
- A deep wrinkle in the skin of the face, especially on the forehead.
- To cut one or more grooves in (the ground, etc.).
- To wrinkle.
- To pull one's brows or eyebrows together due to concentration, worry, etc.