Is Backfill One Word or Two?

backfill verb (MATERIAL)

How do you spell back fill?

material used for refilling an excavation. to refill (an excavation).

How do you use the word backfill?

Backfill sentence example

The backfill was identified as a dark gray clay silt with mixed gravel and lumps of redeposited subsoil. Cover the pipe with some washed stone, and then backfill the trench with soil.