ALDA
nafnorðkvenkyn
u, f.
1. a wave, freq. as a synonyme to bylgja, bára, etc.; it is esp. used of rollers, thus undiralda means the rollers in open sea in calm weather, Edda (Gl.)
2. metaph. in the phrase, skil ek, hvaðan a. sjá rennr undan (whence this wave rolls), hafa mér þaðan jafnan köld ráð komið, veit ek at þetta eru ráð Snorra goða, of deep, well-planned schemes, Ld. 284.
Now used in many COMPDS: öldugangr, öldustokkr.