tile
磚 centers on a flat, hard piece of baked clay used in construction: a tile. The meaning is concrete and specific, without broad abstract extensions.
磚 combines 石 (stone) with 專, which likely contributes the sound and may relate to the idea of a specialized or dedicated piece. The exact historical development is uncertain.
The left side 石 (stone) suggests a hard material, and the right side 專 looks like a compact, rectangular block. Picture a stone-like tile being laid in place.
For セン, imagine a tile with the number 千 (せん, one thousand) stamped on it: 千 -> セン, and the tile is one of a thousand in a roof.