The Spanish word 'dieta' (meaning 'diet' or 'regimen') comes from the Latin word 'diaeta', which meant a 'prescribed way of life'. The Latin term was borrowed from Ancient Greek 'díaita' (δίαιτα), which had a broader meaning of 'way of life' or 'regimen'. This shows how the concept evolved from a general lifestyle or regimen in Greek, to a more specific prescribed lifestyle in Latin, and finally to its modern Spanish meaning focusing primarily on dietary habits and nutrition plans.

The Spanish word 'dieta' is a fundamental term that doesn't have many simpler related words in Spanish. However, you might encounter related terms like 'dietético' (dietary) or 'dietista' (dietitian), which are derived from the same root.

English speakers will easily recognize the connection between Spanish 'dieta' and English 'diet', as they share the same Greek and Latin ancestry. Both languages preserved the core meaning related to food consumption and nutritional regimen. The English word 'diet' can also refer to a legislative assembly (as in 'the Diet of Worms'), which comes from the same etymology but developed this additional meaning through Medieval Latin, where 'dieta' also meant a 'day's journey' or 'day's work', and eventually, a 'meeting'.