Reconstructions

PCS
*rbd - to cover, to put in layers (Kogan 2015: 304)
PCS
*rgm - to stone (Kogan 2015: 217)
See also Proto-MSA *rgm - to cover The reconstruction in HALOT 1187: “The basic meaning develops from ‘to heap up stones’ > ‘to stone’ > ‘to curse’ > ‘to make a statement’” appears highly improbable, especially in its latter step (“to curse” > “to make a statement”)
PCS
*rγṯ - to suck, to suckle (Renfroe 1992:65‒66; Kogan 2015: 321)
exclusive Ugr-Arb isogloss
PCS
*rkk - to be tender, soft, slender (Kogan 2015: 197)
PCS
*rnn - to shout (Kogan 2015: 218)
PCS *rnn ‘to shout’ is likely onomatopoetic. Attestations of this root in Aramaic are rather marginal.
PCS
*rīr-, *rayr- - saliva (SED I No. 234; Kogan 2011: 226)
PCS
*rṣ̂ṣ̂ - to smash (Kogan 2015: 197)
The origin of PCS *rŝṣ̂ ̣ ‘to smash’ is uncertain. Leslau (EDG 529) compares Muh. Msq. Gog. arṭärräṭä, Cha. Gyt. arṭänäṭä, Eža arṭännäṭä ‘to be about to break (wood), to become very old.’
PCS
*si(n)ṭ- - flat hand with wrist (SED I No. 236)
PCS
*šˀr - to remain (Kogan 2015: 198)
PCS
*šby - to take captive (Kogan 2015: 219)