ᴹ✶[tt], [dd] from suffixion became [st], [zd]; [{ttʰd}+t|d+d] > [st|zd]

GS/§4.7 GS/§4.8 GS/§4.9 WG/§87ii [PIE tt > tˢt > Germ/It/Kelt ss] WG/§91ii [PIE dd, td > dᶻd > Kelt zd] @@@

Phonetic Rule Elements

[t+t] > [st]
[tʰ+t] > [st]
[d+t] > [st]
[d+d] > [zd]

Phonetic Rule Examples

rodta- > rosta- d+t > st ᴹ√ROD > ON. rostóbe ✧ Ety/ROD.035
sjadta > sjasta d+t > st ᴹ✶syad-ta > N. hast ✧ Ety/SYAD.053
wedtā > westā d+t > st ᴹ✶wed-tā > N. gwest ✧ Ety/WED.051
wedta- > westa- d+t > st ᴹ✶wed-tā > N. gwesto ✧ Ety/WED.053
kotta > kosta t+t > st ᴹ✶kot-t- > ᴹQ. kosta- ✧ Ety/KOT.017
kotte > koste t+t > st ᴹ✶kot-t- > N. cost ✧ Ety/KOT.013
kʰotʰta > kʰosta tʰ+t > st ᴹ√KHOTH > N. host ✧ Ety/KHOTH.016