Latin -tudo

← Ancient Greek -σῠ́νη (cognate)

← Ancient Greek -δών (mention)

← Proto-Indo-European *-tus (cognate)

← Proto-Indo-European *-h₃onh₂- (mention)

→ French certitude (mention)

→ French -itude (borrowed)

→ Portuguese -itude (borrowed)

→ Portuguese -idão (derived)