antebellum

As a letter s

is the letter s with a.

As an adjective antebellum is

of the time period prior to a war.

As an adjective antebellum

is of the time period prior to a war.

As a noun precursor is

that which precurses, a forerunner, a predecessor, an indicator of approaching events.

As adjectives the difference between bellum and antebellum

is that bellum is while antebellum is of the time period prior to a war.

As a noun bellum

is war.