supine
adj//ˈs(j)uːpaɪn//på rygg, supinum
Lying on its back.
(grammar, also, attributively) (obsolete terminology) The 'to'-prefixed infinitive in English or other Germanic languages, so named because the infinitive was regarded as a verbal noun and the 'to'-prefixed form of it was seen as the dative form of the verbal noun; the full infinitive.