The Spanish verb 'blandir', meaning 'to brandish' or 'to wave (a weapon)', traces its origins back to Old Frankish, a Germanic language spoken by the Franks. It comes from the Old Frankish word 'brant', which meant 'sword blade'. This word evolved into Old French 'brant' meaning 'sword', and then into French 'brandir' meaning 'to brandish'. The Spanish 'blandir' was borrowed from French, with a slight modification where 'r' changed to 'l', a common phonetic change in Spanish.

While 'blandir' doesn't have many common etymologically related words in Spanish, it's worth noting that it maintains a very specific meaning related to the brandishing or waving of weapons or similar objects, staying true to its martial origins.

English speakers might recognize the connection to the word 'brandish', which comes from the same French source 'brandir'. Both 'blandir' and 'brandish' maintain very similar meanings, referring to the action of waving or flourishing something, especially a weapon, in a threatening or showy manner. The English word 'brand' (in its original sense of a burning piece of wood, and later a sword) is also related, though more distantly, coming from the same Germanic roots.