Farther, farthest or further, furthest?
Farther and further are comparative adverbs or adjectives. They are the irregular comparative forms of far. We use them to talk about distance. There is no difference in meaning between them. Further is more common: …

further | American Dictionary

further
adjective, adverb
us/ˈfɜr·ðər/

furtheradjective, adverb (MORE)

more, extra, or additional; comparative offar :
Call your local library for further information.
To further complicate things, I locked my keys in the car.
Not only did I arrive at my conclusions after careful thought, I took a further step and tested them.

furtheradjective, adverb (GREATER DISTANCE)

to a greater distance in space or time; comparative offar :
I can’t run any further.
Read a little further and it will begin to make sense.
further
verb[ T ]
us/ˈfɜr·ðər/

furtherverb[T] (ENCOURAGE)

to help something to succeed; to advance something:
She says the money would be a great help in furthering their cause.

Examples of further

further
The further away any two criteria are from each other in the linguistic hierarchy, the more liberal the system is in permitting such inconsistencies.
A further study, therefore, is planned to reassess these children, after an interval, with myocardial perfusion scans and exercise testing.
Further reference to tools and players is made as the book progresses.
This can best be done in clearly situated case studies, which yield qualitative findings that can then be examined for possible explanations and further enquiry.
This article therefore identifies the need for further research, qualitative and quantitative, on the relationship between women's employment patterns and the dynamics of household formation.
Authenticity arguably has a further dimension, beyond the information and autonomy requirements, namely richness.
The phonetic analysis further bolstered the hypothesis that he added -ed endings according to a pseudo-suffixation strategy.
It is this affective and evaluative progress that teachers might try to develop in pupils in order to develop their skills of musical thinking further.
However, from the mid 1980s the government further reduced the municipal elbowroom.
No further gains were achieved in the last decade of the century, during which the third- and fourth-generation cultivars replaced the original introduced cultivars.
The problem can be further generalized by replacing the indicator function by a smooth approximation.
To probe this issue further, workers were requested to list the things they liked about their companies and things they did not like.
Suppose further that, in response to some past wrongdoing, an omnipotent being changes one of the numbers on the winning ticket.
For all farm categories, current acreage increased from 5 years in the past, and farmers predicted further increases in the future.
Could one overcome the threat to the interest theory by arguing that interests are ranked only by their contribution to further interests?
These examples are from corpora and from sources on the web. Any opinions in the examples do not represent the opinion of the Cambridge Dictionary editors or of Cambridge University Press or its licensors.