*flataz

Uncertain. (Rychło 2017) proposes a derivation from Proto-Indo-European **plod-sk-o, (presumably based on Pokorny’s marginal *plā̆d- (‘broad and flat, spread out’)) for this word and potential cognate in Slavic (e.g. Polish płaski (‘flat’)). This works for Proto-Germanic but poses issues for Balto-Slavic. Kroonen’s (2013) derivation from *pleth₂- (‘to spread, extend; flat’) requires a pre-Germanic geminate, **plottos < *ploth₂-nó-s (via Kluge's law) that is later degeminated (a non-geminate derivation from this root would provide the wrong final consonant, -þ). However, the morphological gymnastics of geminating then degeminating makes this derivation somewhat suspect. (Watkins 2011), based on (Pokorny 1959), posits the simplest derivation from PIE root *plad- as a simple “variant form” of *pleth₂-.The issue here is the lack of cognates with a similar voiced dental.