Words for parts and related words in Celtic languages.

Proto-Celtic	*rannā = part
Old Irish (Goídelc)	rann = part (of a whole) randatu = the property of belonging to a part of speech rannaid = to divide (into parts), to apportion ranngabáil = participle
Irish (Gaeilge)	rann [ɾˠanˠ] = part, side (in dispute), partition rannach = apportioning, sharing, open-handed rannadóir = divider, sharer rannán = division rannóg = section rannpháirt = participation, part, share roinn = share, portion, distribution, dealing, trading, division
Scottish Gaelic (Gàidhlig)	rann [r̪ˠaun̪ˠ] = stanza, quatrain, verse, bond, deed, division, part, portion, section rann-phàirt = participation, portion, participle roinn [r̪ˠɤin̪ʲ / r̪ˠɤn̪ʲə] = dividing, partitioning, section, share, allotment, partition, department, division roinneadair = divider, divisor, sorter
Manx (Gaelg)	rheynn = divide, classify, distribute, dispense, share fo-rheynn = section so-rheynn = divisible
Proto-Brythonic	*rrann = part
Middle Welsh (Kymraec)	rann = part
Welsh (Cymraeg)	rhan [r̥an] = part (of something), portion, division, element, constituent, component rhanadwy = divisible, dividend rhanedig = shared (out), divided, parted, split, separate rhannu = to divide, separate, part, divide
Old Cornish	radn = part, portion
Cornish (Kernewek)	radn = lot, part, portion, role, share
Breton (Brezhoneg)	rann = part, division, fraction, fracture, split

Etymology: from the Proto-Indo-European *per- (to sell) [source], which is also the root of such English words as depart, jeopardy, parcel, part, partition and portion [source].

Words marked with a * are reconstructions.

Sources: Wiktionary, Am Faclair Beag, Online Manx Dictionary, Teanglann.ie, eDIL – Electronic Dictionary of the Irish Language, logainm.ie, In Dúil Bélrai English – Old Irish glossary, Geiriadur Prifysgol Cymru, Gerlyver Kernewek, Dictionaire Favereau, TermOfis, English – ProtoCeltic WordList (PDF), Etymological Dictionary Of Proto Celtic