The Spanish verb 'empezar' (to begin) has an interesting formation that combines Latin and Celtic elements. It was constructed from the Latin prefix 'in-' (meaning 'in, into'), combined with the Spanish noun 'pieza' (meaning 'piece'), which itself comes from the Celtic word 'pettia' (meaning 'piece'). The verb was then formed by adding the Spanish infinitive suffix '-ar'.

The semantic evolution from 'piece' to 'begin' likely developed from the concept of 'getting into a piece of something' or 'taking the first piece', which naturally evolved to mean 'to start' or 'to begin'.

A simpler and very common Spanish word related to 'empezar' is 'pieza' (piece), which you can see is directly incorporated into the verb 'empezar'. While 'pieza' retained its original meaning of 'piece' or 'part', when combined with the prefix 'em-' (from Latin 'in-') and the verb suffix '-ar', it developed into the concept of beginning or starting something.

While English 'piece' and Spanish 'pieza' both ultimately come from the same Celtic root 'pettia', they entered the languages through different paths - 'piece' came through Old French, while 'pieza' came directly from Celtic into Vulgar Latin and then Spanish. This shared ancestry explains why 'piece' and 'pieza' sound similar and mean the same thing, though 'empezar' developed its own unique meaning of 'to begin'.