*ardugaz

From Proto-Indo-European *h₃érdʰu-ko-s from the u-stem adjective *h₃érdʰ-u-s ~ *h₃r̥dʰ-éw-s, from root *h₃erdʰ-, further extended in pre-Germanic with adjectival *-ko-s (Kluge 1899: § 206; Kroonen 2013: 33–34; Krahe & Meid 1969: 192). The *-dʰ- may represent a PIE root enlargement of root *h₃er- , traditionally called the dʰ-determinative, in Germanic nouns derived from intransitive roots. Lehmann (1942: 126) analyzes this enlargement as marking a state or result produced by a preceding action. Cognate with Ancient Greek ὀρθός (orthós), Sanskrit ऊर्ध्व (ūrdhvá), Proto-Celtic ardwos, and Latin arduus (Beekes 2010: 1101; de Vaan 2008: 52; Matasović 2009a: 40–41). Garnier (2014a: 28–29) instead regards the *-gaz extension as a specifically Germanic innovation from the inherited u-stem rather than an inherited PIE derivative