Etymology
1. From Middle English treowe, trew, trewe, triwe, true, trwe, from Old English trēowe, trīewe (“faithful, true”), from Proto-Germanic *triwwiz (“faithful, true”), from pre-Germanic *drewh₂yos, from Proto-Indo-European *drewH- (“firm, hard, true”).
2. Cognates
3. Cognate with Saterland Frisian trjou (“honest”), Alemannic German trüüw (“loyal”), Dutch trouw (“loyal, true”), German treu (“loyal, true”), Luxembourgish trei (“loyal”), Danish tryg (“safe, secure”), Faroese and Icelandic tryggur (“faithful, loyal; safe”), Norwegian Bokmål, Norwegian Nynorsk, and Swedish trygg (“safe, secure”), Gothic 𐍄𐍂𐌹𐌲𐌲𐍅𐍃 (triggws, “true; faithful, loyal”); also Irish dearbh (“sure”), Old Prussian druwis (“faith”), Ancient Greek δροόν (droón, “firm”)), extension of *dóru (“tree”) (possibly also Proto-Slavic *sъdorvъ (“healthy”) from the same root). More at tree. For the semantic development, compare Latin robustus (“tough”) from robur (“red oak”). See: Middle English Nouns '
treowe', Old English Nouns '
trēowe', Dutch Nouns '
trouw', Latin Nouns '
robustus'.