From Greek 'barys' (heavy) + 'tonos' (tone) — literally 'heavy-toned,' sharing 'barys' with 'barometer' and 'barium.'
From Italian 'baritono,' from Greek 'barýtonos' (βαρύτονος, 'deep-sounding'), a compound of 'barýs' (heavy, deep) + 'tónos' (tone, tension, pitch), from PIE *gʷrh₂-ú-s ('heavy') + *ten- ('to stretch'). The PIE root *gʷerh₂- ('heavy') is the ancestor of Latin 'gravis' (heavy, serious—giving English 'gravity,' 'grave,' 'grief'), Sanskrit 'gurú-' (heavy, weighty—giving 'guru'), and Gothic 'kaúrus' (heavy). The second element, *ten- ('to stretch'), produced Latin
'Baritone' (heavy-tone) and 'barometer' (heavy-measure, i.e., pressure-measure) share Greek 'barys' (heavy). A baritone voice has 'weight.' A barometer measures atmospheric 'weight.' And 'barium' (the element) was named for its heavy compounds. The same heaviness connects a singing voice, weather prediction, and a chemical element.