The most common and most likely answer to this crossword clue is the 4 plus 5 plus 2 plus 4 letter word FROM FIRST TO LAST
I've seen this crossword clue in The Daily Telegraph
F
R
O
M
F
I
R
S
T
T
O
L
A
S
T
Buddy explains!
The straight part
We know that "throughout" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case throughout = from first to last.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.