The most common and most likely answer to this crossword clue is the 6 letter word ASHLAR
I've seen this crossword clue in The Guardian
A
S
H
L
A
R
More clues leading to the result ASHLAR
- Demolishing wings, smash large masonry
- Seen in pebbledash, large piece of masonry
- Building block of wood, what’s backed with board in port
- Some potash largely fashioned masonry
- Th ose naughty kids have got involved in ark
- Stone remains, article clutched in both hands
- One sort of wood and another with church lacking stonework
- Absorbed by cash; Lara Stone
- Tree god’s made of stone
- Beside the world tree god creates squared stone
Buddy explains!
The straight part
We know that "Building block" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case building block = ashlar.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 ASHLAR mean?
ASHLAR noun- A large cuboid stone; masonry making use of such stone blocks.
- A hurling stone used in warfare.