An Etymological Dictionary of the German Language/Wank
Wank, m., in the phrase ohne Wank, ‘without hesitation,’ MidHG. âne wanc, OHG. âno wanc; MidHG. wanc, m., ‘want of stability, fickleness.’ Allied to wanken, vb., ‘to totter, vacillate, hesitate,’ from MidHG. wanken, OHG. wanchôn, ‘to totter, waver’; comp. OIc. vakka (for *wankân), ‘to totter.’ Connected with OHG. wanchal, MidHG. wankel, ‘wavering, fickle’ (hence Wankelmut, m., ‘vacillation,’ MidHG. wankelmuot); allied to winken.