Note: 'Furthest' is a superlative form of 'far'.
1.
Furthest means to a greater extent or degree than ever before or than anything or anyone else.
The south of England, where prices have fallen ~, will remain the weakest market...
These institutional reforms have gone ~ in Poland.
ADV: ADV with v
2.
Furthest means at a greater distance from a particular point than anyone or anything else, or for a greater distance than anyone or anything else.
The risk of thunder is greatest in those areas ~ from the coast...
Amongst those who have travelled ~ to take part in the Festival are a group from Northern Ireland.
ADV: n ADV, ADV after v, be ADV, ADV prep/adv
•
Furthest is also an adjective.
...the ~ point from earth that any controlled spacecraft has ever been.
ADJ: ADJ n