The name Cardolan appears to be Sindarin for "Red Hill Land". In that case, the name could be analyzed as caran "red", dol "hill" and the toponymial ending -(i)an.
Sindarin
cardolan
place name. ?Red Hill Land
Elements
Word Gloss caran “red” dol(l) “head, hill” -ian(d) “-land, country”
Cardolan
Red Hill Land
Cardolan
Cardolan
It is not known if Tolkien ever explained the name Cardolan. The most common suggestion is that Cardolan likely is Sindarin for "red hill country". In that case, the name could be analyzed as carn "red", dol "hill, mount" and an(n) "land". An alternative etymology has been suggested by Roger Clewley: Cardolan deriving from Noldorin car "house", dolen "hidden, secret", and the toponymical ending -and, thus meaning "place/land of hidden houses" (a reference to the "dead entombed there").
The southernmost of the successor-realms of Arnor after it was divided into three kingdoms (LotR/1039). Tolkien did not translate the name, but it is often interpreted as “Red Hill Land”, as suggested by Hammond and Scull (RC/690) or David Salo (GS/371), a combination of caran “red”, dol(l) “hill” and the suffix -(i)an “land”. @@@ Originally suggested by Robert Foster, need ref.