The most common and most likely answer to this crossword clue is the 4 plus 5 letter word FULL BOARD
I've seen this crossword clue in The Daily Telegraph
F
U
L
L
B
O
A
R
D
More clues leading to the result FULL BOARD
Buddy explains!
The straight part
We know that "Pension" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case pension = full board.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.