The name apparently contains girith "shivering" and raun "moon, month".
Sindarin
girithron
noun. december (month)
girithron
noun. December, *Shuddering-one
Cognates
- Q. Ringarë “December, *Coldness” ✧ LotR/1110
Elements
Word Gloss girith “shuddering, shuddering; [N.] horror” -(r)on “agental suffix”
girithron
december
girithron
Girithron
girithron
december
(na ’Irithron)
Girithron (na **Irithron**)