The Spanish word 'tortilla' comes from adding the diminutive suffix '-illa' to the Spanish word 'torta', meaning 'flat bread' or 'cake'. Going further back, 'torta' derives from the Greek word 'artidion', meaning 'small bread', which itself comes from the Greek root 'artos' meaning 'bread'. Over time, as the word traveled from Greek through various language changes, the initial 'a-' sound shifted to 't-', giving us the modern Spanish form.

The most obvious related Spanish word is 'torta', which generally refers to a larger flatbread, cake, or sandwich depending on the region. While 'tortilla' specifically refers to the small, round flatbread (typically made from corn or wheat flour) that's so fundamental to Mexican cuisine, 'torta' is its "bigger sibling" - the relationship between these words is very straightforward since 'tortilla' literally means 'little torta'.

While English has borrowed the word 'tortilla' directly from Spanish, there aren't many common English words that share the same ancient Greek root 'artos'. However, this Greek word for bread does appear in some specialized English terms like 'artology' (the study of bread and baking) and 'artolatry' (bread-worship), though these are quite rare and technical terms.