The Spanish word 'ruco' meaning 'old' or 'elderly' appears to be a colloquial or slang term. While its exact etymology is uncertain, it is commonly used in informal Mexican Spanish and some other Latin American varieties.

Some Spanish speakers might associate 'ruco' with other informal terms for old age like 'viejo' or 'anciano', but there are no clearly related simpler Spanish words that share a definitive etymological connection.

There are no clearly related English words that share an etymological connection with the Spanish slang term 'ruco'.