Plenty of people have written bigger and better things about Tolkien's inspirations from Norse myth, Anglo-Saxon culture, Finnish and Welsh languages, and Beowulf. I'm not going to try to one-up them, but here are a few translations and definitions:
NOTE: In cases where a definition or translation couldn't be found, I quoted the OE text of 'Beowulf' directly.
Beowulf Influences:
The Mark - from MERCIA or MYRCE, the central kingdom of the Anglo-Saxons
Edoras- from EODERAS, line 1037: "in under eoderas; para anum stod"
Meduseld - from MEAD-HALL, line 3065, Beowulf's own hall
Ents - from ENTA, "giants," line 2717: "enta aergeweorc"
Ents - also from EOTENAS, line 112: "ogres"
Orcs - from ORCNEAS, line 112: "evil phantoms"
Orthanc - "skill, ingenuity"
Beorn - from BEORN, line 1299, "warrior"
Hama - from HAMA, line 1198, a great treasure-hoarder who "snatched the Brosings' neck-chain and bore it away"
Elf - from YLFE, line 112: "elves"
Middle-earth - from MIDDAN-GEARD, line 75: "middle-earth" or "wide earth"
Names from Beowulf:
Eorl - from EORL, line 573: "undaunted courage"
Freawine - from FREA-WINE, line 2357: "people's friend and lord"
Brego - from BREGO, line 609: "prince"
Theoden - from ÞEODEN, line 1871: "high-born" (referring to Hrothgar)
Eomer - from EOMER, line 1960: "from him there sprang Eomer, Garmund's grandson, kindman of Hemming, his warriors' mainstay and mater of the field"
Goldwine - from GOLD-WINE, line 1171: "open-handed" or "generous" (as in he who gives out gold)
Frea - from FREA, line 2285: "master"
The big deal here is that the language and culture of Rohan is a strange blend of both Old Norse and Old English. The Anglo-Saxons spoke Old English, which 'Beowulf' was originally written in, but the story of Beowulf is about Vikings, who spoke Old Norse.
As a result, both cultures (Anglo-Saxon and Viking) are represented and reflected upon. This is how Tolkien built Rohan and its people--by side-stepping his role as "fictionalist" and adopting a more suitable and more culturally believable role as "historian."
So if someone asks you, the people of Rohan are parallel to the language of 'Beowulf'--they are neither Anglo-Saxon nor Viking, but a mutually-commentative blend of both.
Of course, the one for-sure thing in all of this is that Rohan is NOT Celtic! :-)
November 2001: translations gleaned from Seamus Heaney's 2000 edition of Beowulf