so·lum 
(sōləm)
(sōləm)n. pl. so·la (-lə) or so·lums
The upper layers of a soil profile in which topsoil formation occurs.
[Latin, base, ground.]
- transpontine
- transport
- transportability
- transportable
- transportation
- transporter
- transportive
- transposable
- transpose
- transposition
- transpositional
- transposon
- transracial
- transsexual
- transship
- transshipment
- transthoracic
- transthoracically
- transubstantiate
- transubstantiation
- transubstantiationalist
- transudate
- transudation
- transudatory
- transude