The most common and most likely answer to this crossword clue is the 6 letter word PLINTH
P
L
I
N
T
H
More clues leading to the result PLINTH
Buddy explains!

The straight part
We know that "projection" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case projection = plinth.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 PLINTH mean?
PLINTH noun- A block or slab upon which a column, pedestal, statue or other structure is based.
- The bottom course of stones or bricks supporting a wall.
- A base or pedestal beneath a cabinet.