Cartherit or Cartheril, an old name for Castlerigg near Keswick (with a side trip to Arthuret)

Cartherit, appears to be an older name for Castlerigg NY277227. It appears on Ogilby's map of 1675.  It appears as Cartheril on Bowen & Kitchen's map of 1760.  Possibly both from an older map? I am tempted to see Cumbric caer here, where caer equates to the  Castle-  in Castlerigg. The Low Nest Farm website discusses the location of Cartherit. It says that the Castle refers to the Castlerigg Stone Circle or the Roman fort that was adjacent to it. The Low Nest farm with local knowledge say later maps change Cartherit to Brow Top, i.e. the top of Nest Brow. So, Caertherit might have been the Cumbric name for the settlement enear Castlerigg stone circle (and Roman fort ruins). The text accompanying Ogilby's map says "Then descending pass thro' Cartherit-V (i.e. village), and at 29'4 (miles from Kendal) to Keswick…"

 -therit is more difficult to interpret than caer. Firstly consider Welsh terydd, "ardent, furious" (see James, 2016). This has been proposed as the second element of Arthuret NY378674. Arthuret is supposed to be the site of the Battle of Armterid where Gwenddolau fought Peredur and Gwrgi and Rhydderch Hael of Strathclyde in 573. This has been interpreted as Arf + Terydd "swift or terrible weapon/arms". James pefers ardd "height" + terydd, which makes more sense as the church stands on a bluff above the River Esk. I find it difficult to see terydd in a place name, unless perhaps a river name, "ardent, furious". The Esk is the Celtic name, Terydd, could have been the local name for that stretch of the river. 

 Caer + terydd would give Caerderydd not *Caerdderydd. The -t could be explained because Old English had no /-ð/ and substituted /-d/ cf. Minehead and Long Mynd, both from mynydd. The final /-d/ would be devoiced as normal to /-t/ in Scots/Cumberland English. But I am struggling to find an element that fits this in Welsh, Cornish or Breton.
 
However, if, Carithet refers to the stone circle or the Roman ruins, we would expect the second element to elaborate on it. Another version of the name is Catheril 1760. This might allow us to see the name as  Caerddryll where dryll has two meanings - "fragment" or "spear, javelin" (in Modern Welsh it means gun).  The Melville Richards archive gives various Welsh place-names with dryll, e.g Cae Dryll y Maen Llwyd near Llanwyddan, Byr Ddrylliau near Arllechwedd, Beudy Drylliau - all in Caernarfonshire, Allt y Dryll near Fishguard in Pembrokeshire. In most of these the meaning seems to be "fragment", apart from the last where it could well be "spear".  So Caerddryll would mean Fort of the Spear, which is equivalent to Dunpelder in East Lothian and similar to Drumpellier in Lanarkshire.

 Cartheril - Caer Ddryll - "Fort of the Spear", or "Fort in Bits."

 Phonologically /kairðrɨɬ  > English karðəril ~ karθəril/ with the name later replaced by English Castlerigg.