adverb, adjective, and verb
Note: Some usage guides insist that only farther describes physical distance (We walked farther than we planned). But farther and further have been used interchangeably throughout much of their histories.
Note, however, that only further may be used in the adverbial sense of “moreover” (Further, you hurt my feelings) and in the adjectival senses of “more extended” (no further comment) and of “additional” (Further bulletins came in).
Grammar.com’s section on Problem Words discusses further and farther. Click here for that discussion.
Example: Let’s not discuss it further. adverb
Example: I have no further comment. adjective
Example: He wanted to further his career. verb
Example: He walked farther down the road. adverb