Probably from guwd; a thong (as compressing); by analogy, a tendon -- sinew.
see HEBREW guwd
H1517. gid
גִּיד noun masculineGen 32:33 sinew (Late Hebrew id., Aramaic גִּידָא, ; compare Arabic neck) — construct גִּיד Genesis 32:33 (twice in verse); Isaiah 48:4; plural גִּידִים Job 10:11; Ezekiel 37:6, גִּדִים 37:8; construct גִּידֵי Job 40:17; — sinew, in General of human body, "" עצמות עור, בשׂר,, 10:11 compare Ezekiel 37:6, 8 of thigh Genesis 32:33 (of beast) 32:33; iron sinew, figurative of obstinacy, Isaiah 48:4 ׳וג נְחוּשָׁה וּמִצְחֲךָ עָרְמֶּ֑ךָ בַּרְזֶל; of hippopotamus, ׳ג פחדו, i.e. of his loins, Job 40:17.