I ran across the Spanish word rueca ‘distaff’ and (as is my wont) wondered where it had come from. That turns out to be a more difficult question to answer than one might think. I first turned to the Diccionario de la lengua española, which said laconically “(Del germ. *rŏkko).” With that to go on, Google Books got me a view of p. 110 of Encyclopedia of Indo-European Culture, by James Mallory and D. Q. Adams, with the entry:
*ruk- ‘over-garment’. [IEW 874 (*ruk(k)-); Wat 55 (*ruk-)]. Olr rucht (< *ruktu-) ‘tunic’, MWels ruch(en) (< *roukkā) ‘cloak’, OE rocc ‘over-garment, rochet’, OHG rocko ‘distaff, Goth *rukka (borrowed into Italian rocca ‘distaff’) (< Gmc *rukkōn). An isogloss of the western periphery of the IE world.
Which sounded reasonably convincing, except that I wasn’t sure why a word for ‘over-garment’ would turn into one for ‘distaff.’ Investigating further, I learned there was an archaic English word for ‘distaff,’ rock, first attested in the fourteenth century (a1325 in G. H. McKnight Middle Eng. Humorous Tales (1913) 23 “Wit my roc y me fede; Cani do non oyir dede”), whose entry, happily for me, had just been updated in June 2010. The long etymology says everything that can be said at present about the history of this difficult word:
Either cognate with, or perhaps borrowed < one of, Middle Dutch rocke, (in late sources, probably from inflected forms) rocken (Dutch rokken, †rok), Middle Low German rocke, Old High German roc, rocco, roccho, rocho (Middle High German rocke, German Rocken), Old Icelandic rokkr, Norwegian rokk, Old Swedish rokker (Swedish rock), Old Danish rooc (Danish rok), all in sense ‘distaff’; further etymology uncertain and disputed (see below). Compare Old Occitan roca (c1250), Spanish rueca (13th cent.), Portuguese roca (15th cent.), Italian rocca (a1321).
The dominant view is that the Romance words represent early borrowings from the base of the Germanic words, more specifically, from an unattested Gothic form *rukka (which would have diffused with the Visigoths in Italy and Spain). However, while this view poses no phonological problems for the Occitan and Italian words, it encounters difficulties with regard to the Spanish and Portuguese words, since these presuppose a common ancestor with open o (which regularly diphthongized in Spanish), which is difficult to reconcile with the suggested Gothic etymon, and equally difficult to explain as a borrowing from West Germanic. It has been suggested that the different vowel quality in Spanish and Portuguese (which is paralleled outside the Iberian peninsula by Rhaeto-Romance) might be explained by influence of the classical Latin synonym colus (see colulus n.). In addition, if the word is held to be originally Germanic, its further etymology is unclear, as no fully convincing cognates have been found for the Germanic words (a connection with the Germanic words cited at rochet n.1 has sometimes been suggested, but is very doubtful). See further J. Corominas Diccionario crítico etimológico castellano e hispánico (1981) at rueca, with detailed discussion.
An alternative etymology derives both the Germanic and the Romance words from an unattested post-classical Latin form *rotica , a derivative of classical Latin rota wheel (see rota n.) or rotāre rotate v., the distaff being so called on account of its rotating motion. However, this etymology is not generally accepted.
There is a set of obsolete English names for more or less the same post-Christmas day [thanks, iakon!]: Rock Day was “the day after Epiphany (i.e. January 7th)”; Rockfeast was (in Norfolk) “a festival following Epiphany, traditionally the day on which women resume their spinning and other tasks after the Christmas holidays”; and Rock Monday was “the first Monday after Epiphany, traditionally the day on which women resume their spinning and other tasks after the Christmas holidays, marked in certain parts of the country by various festivals and other customs.”
I might also point out the charming (and obsolete) Scots expression to come over with one’s rock, meaning ‘to make a social visit’: 1793 J. Sinclair Statist. Acct. Scotl. VII. 613 “When one neighbour says to another,..‘I am coming over with my rock,’ he means no more than to tell him that he intends soon to spend an evening with him.” (Note the masculine pronouns, striking in the context of the common use of distaff to refer to women and their concerns.)