†a-ˈthester,v.Obs.[OE.aþéostrian,f.a- prefix 1 + þéostrian: see thester v.]To grow dim, darken, become obscure.c885K. ælfredBoeth. ix,Þonne aðéostriaþ ealle steorran.c1175Cott.Hom.239Si sunne and se mone aþestreð for godes brictnesse.1205Lay.2860Enne blase of fure, Þe neuer ne aþeostrede.