In late PIE (i.e. post-Anatolian period) the word metathesized into *h₂ŕ̥ḱtos which phonetically surfaced as *h₂ŕ̥ḱþos following the rule that when dental and velar occlusives appear syllable-initially, they metathesize tk → kt and turn into a thorn cluster denoted ḱþ. See Wikipedia for a discussion of these clusters' makeup.
*h₂ŕ̥tḱos m (non-ablauting)
- Hittite: 𒄩𒅈𒋫𒀝𒂵𒀸 (ḫartaggas) "bear-clad dancer"
- Lithuanian: irštva (“bear’s den”) (< *h₂ŕ̥tḱo/eh₂)
- Celtic: *artos (see there for further descendants)
- Indo-Iranian: *Hrtća
- West Iranian
- East Iranian
- Kamviri: ic
- Latin: ursus (< *orssos < *orksos) (see there for further descendants)