Subter

Preposition used with Accusative and Ablative.
The circumflected accents are used to mark the vowels' length.

with Accusative
 

It is used in prose: under

• Decius subter togam manum ad mentum tulit.

Under the garment Decius brought his hand to the chin.

with Ablative
 

It is used in poetry: under

• sub densa testudine  under a thick moveable shed.