sine: [16] As in the case of many other mathematical terms, English is indebted to Arabic for sine. But here the debt is only semantic, not formal. The word sine itself was borrowed from Latin sinus ‘curve, fold, hollow’ (source also of English sinuous [16] and indeed of sinus [16], whose anatomical use comes from the notion of a ‘hollow’ place or cavity). In postclassical times it came to denote the ‘fold of a garment’, and so it was mistakenly used to translate Arabic jayb ‘chord of an arc’, a doppelganger of Arabic jayb ‘fold of a garment’. => sinuous, sinus
