furlongyoudaoicibaDictYouDict
furlong: [OE] Furlong ‘eighth of a mile’, which has now virtually died out except in horse-racing terminology, is part of a vocabulary of lengthmeasuring bequeathed to us by the agricultural practices of our ancestors. It originated as an Old English compound formed from furh ‘furrow’ and lang ‘long’ – that is, the length of a furrow ploughed across a standard-sized square field of ten acres.

Since the term acre varied somewhat in its application at different times and places, the length of a furlong could not be computed with great precision from it, but in practice from about the 9th century the furlong was pegged to the stadium, a measure equal to one eighth of a Roman mile.
=> furrow, long
peg (v.)youdaoicibaDictYouDict
"fasten with or as if on a peg," 1590s, from peg (n.). Slang sense of "identify, classify" first recorded 1920. Related: Pegged; pegging.