From 𐌲𐌹𐍃𐍄𐍂𐌰- (gistra-, compare yester-) + *𐌳𐌰𐌲𐌹𐍃 (*dagis, “by day”, adverbial form of 𐌳𐌰𐌲𐍃 (dags)). Alternatively, the compound may be an adverbial form of an unattested noun *𐌲𐌹𐍃𐍄𐍂𐌰𐌳𐌰𐌲𐍃 (*gistradags, “tomorrow”).
𐌲𐌹𐍃𐍄𐍂𐌰𐌳𐌰𐌲𐌹𐍃 • (gistradagis)