Borrowed fom Latin magnus 'id.'
From Proto-Italic *magno- 'id.' From Proto-Indo-European *m̥ǵ-no- 'id.' From the root *meǵh2- "much."
Also the origin of the surname Magnet.
Romance: Western Vulgar Latin: Portuguese magno, Italian magno
Indo-European: Celtic: Gaulish Magios (name) "great," Middle Irish maige "large;" Gothic: Gothic mikils "large," Old Norse mikill 'id.,' Old High German mihhil 'id.,' Old Saxon mikil 'id.,' Old English micel 'id.' (Middle English muchel, English much); Albanian: madh "large;" Hellenic: Ancient Greek μέγας (mégas) "large;" Armenian: mec "large;" Indo-Iranian: Sanskrit máhi- "large," Avestan mazōi "big;" Tocharian: A māk "many," B māka 'id.;' Anatolian: Hittite mekk- "much," Cuneiform Luwian maia- "many"