The most common and most likely answer to this crossword clue is the 10 letter word TRIANGULAR
I've seen this crossword clue in The Daily Telegraph
T
R
I
A
N
G
U
L
A
R
More clues leading to the result TRIANGULAR
- Without question, Qatar ruling is amended with several points?
- Like warning signs Alan Turing devised, changing number for radius
- Stated aim by ‘Bony’, in formation of three lines
- Deciphering unfinished Alan Turing rule initially concerning the numbers 0, 1, 3, 6, 10…
- Gran joins ritual dancing involving three people?
- Organised a trial run with group's chief, involving three stakeholders
- Same as trigonal
- Like a frame of snooker?
Buddy explains!
The straight part
We know that "formation of three lines" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case formation of three lines = triangular.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 TRIANGULAR mean?
TRIANGULAR adjective- Shaped like a triangle.
- Of, or pertaining to, triangles.
- Having a triangle as a base; as, a triangular prism, a triangular pyramid.
- Having three elements or parties; trilateral, tripartite.