The Common Speech is the language spoken by most people in Middle-earth. The speakers of the language call it Yandūnë (which means Westron) or Sōval Phārë (which means Common Speech). In the Lord of the Rings it is represented by Modern English.
Some words in in the Common Speech are only used by the hobbits of the Shire or by people of Bree, for example the word kuduk (hobbit).
The language of Rohan (represented by Old English) is similar to the Common Speech, and it could be called an antique form of the Common Speech. Although the two languages started in a similar area, the language of the Rohirrim was more isolated in the north and had changed much less.
Ban - half, almost
Banakil - halfling
Bophan - Boffin
Bolg - bulge
Bolgra - Bolger
Bralda - heady
Brand - foam
Branda - border
Brandagamba - Brandybuck
Cot-tūn - cotton
Galab - game
Galbasi - Gamgee
Hîm - ale, beer
Hloth - a two roomed dwelling or hole
Hlothram - cottager
Hlothran - Cotton
Hamanullas - small, blue garden flower (gardener’s name)
Kali - happy
Karningul - Rivendell
Kast - mathom
Kuduk - hobbit (shire only)
Labin - bag
Labin-nec - Bag End
Labingi - Baggins
Luthur - down, fluff
Maur - wise (old word)
Mumak - Oliphant
Narac - dwarf
Nec - end
Nin - water
Phārë - speech
Phūru - Delve
Ran(u) - a group of small two roomed dwellings on a hill
Raspūta - Hornblower
Raza - stranger
Razan - foreign
Razar - a small red apple
Sōval - common
Sūza - Shire
Tapuc - rabbit
Tharni - quarter (old word)
Tharantīn - fourth part
Trān - digging, burrowing
Tūk - Took
Tung - big
Yandūnë - Westron
Zara - old
Zaragamba - Oldbuck
Zilib - butter
Zir - wise
References:
J.R.R Tolkien, The Return of the King, Appendix F, On Translation
Christopher Tolkien, The History of Middle-Earth, The Peoples of Middle Earth, The Appendix on Languages