1. Furthest towards the south.

2. Farthest south.

Nuttall's Standard dictionary of the English language By Nuttall, P.Austin

• southermost,
• aouthernmost,
• zouthernmost,
• xouthernmost,
• douthernmost,
• eouthernmost,
• wouthernmost,
• siuthernmost,
• skuthernmost,
• sluthernmost,
• sputhernmost,
• southerrnmost,
• southernmmost,
• southenmost,
• southernmst,
• Southemost,
• southernmoste,
• southennmost,
• southemmost,
• southermostt

• southern porgy,
• southern scup,
• southernness,
• southern cross,
• southern aster,
• southerner,
• southern beech,
• southern lights,
• southern tai,
• southernism,
• southernwood.

The adjective form of the word "southernmost" is "southern".

The plural form of "southernmost" is "southernmosts". However, it is worth noting that the usage of this plural form is rare and most commonly, the word is used in its singular form.

The singular form of the word "southernmost" is "southernmost". The word does not change in form for singular or plural usage.