The most common and most likely answer to this crossword clue is the 9 letter word CROSSBEAM
I've seen this crossword clue in Financial Times
C
R
O
S
S
B
E
A
M
More clues leading to the result CROSSBEAM
Buddy explains!

The straight part
We know that "extending from one side to the other" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case extending from one side to the other = crossbeam.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 CROSSBEAM mean?
CROSSBEAM noun- A horizontal structural beam that runs perpendicular to the primary support beams; a girder.
- A beam laid across the bitts, to which the cable is fastened when riding at anchor.