fyrretyve.

Older form of fyrre. From Old Danish fyritiughu, from Old Norse fjórir tigir, from Proto-Germanic *fedwōr tigiwiz (“forty”, literally “four tens”), cognate with Norwegian førti, Swedish fyrtio, English forty, German vierzig, among others. Note that the suffix -tyve in fyrretyve means “ten”, unlike the word tyve (of different origin: from Old Danish tiughu, from Old Norse tuttugu, from Proto-Germanic *twai tigiwiz (“twenty”, literally “two tens”)), which means “twenty” and which also forms part of the dated forms of the higher tens: halvtredsindstyve (“fifty”, literally “two and a half times twenty”), tresindstyve (“sixty”, literally “three times twenty”) etc.