A (ab, abs)

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

Forms:

The form a is used before consonants, and the form ab before vowels, but sometimes before consonants also; abs is used in the expression abs te by you.
The preposition denotes separation or distance from periphery (surface) of an object / person and not from interior (cf. ex).
 

Non figurative usage

1. Space: from

• Plebei ab urbe secedunt.

The plebeians withdraw from the city (of Rome).
• Romani impetum hostium ab laevo sustinere non potuerunt.

The Romans were not able to sustain the attack from the left.

• ab urbe condita (A.U.C.)  since the City (of Rome) was founded

Figurative usage

1. Agent (in the passive voice): by

• Decius ab exercitus corona civica donatus est.

Descius was granted a civic crown by the army.

• ab odio  for hatred
• ab ira  for wrath