sub-

1. Below; under; beneath: subsoil.
2. 1. Subordinate; secondary: subplot.
   2. Subdivision: subregion.
3. Less than completely or normally; nearly; almost: subhuman.

[Middle English, from Latin, from sub, under.]

1. Below; under; beneath: subcutaneous.
2. Subordinate; secondary: subinfection.
3. Subdivision: subkingdom.
4. Less than completely or normally; nearly; almost: subfertility.