'argentinean' ultimately derives from the country name 'Argentina', which in turn comes from Latin 'argentum' meaning 'silver'.

'argentum' (Latin) gave rise to Spanish 'Argentina' (used for the region associated with the Río de la Plata), and English formed the adjective/noun 'Argentine'/'Argentinian' and the variant 'Argentinean' from that country name.

Originally associated with 'silver' through Latin 'argentum', the term evolved to name the geographic region and then people or things 'from Argentina'; its modern meaning is 'from or relating to Argentina'.