Below, under, beneath, underneath mean in a lower position relatively to some other object or place.
Below (opposed to above) applies to something which is anywhere in a lower plane than the object of reference; under (opposed to over) to something which is below in a relatively vertical line, and it may imply actual covering.
Underneath is often employed in place of under or beneath. It is, however, the preferred term when there is the intent to imply complete or nearly complete concealment.
In their extended senses below and under agree in expressing inferiority but differ (like above and over) in the immediacy of the relation expressed; thus, one officer may be below another in rank without being under him in immediate subordination.
Similarly, with reference to deficiency, below is commonly used in general, under in more specific, relations.
Beneath frequently suggests social, moral, or general inferiority.
Underneath suggests, not inferiority, but something underlying and not indicated clearly by what is outwardly manifest.