The Spanish word 'boca' (meaning 'mouth') comes from the Latin word 'bucca', which meant both 'cheek' and 'mouth'. The Latin term itself appears to have Celtic origins, derived from Proto-Celtic 'bocca' meaning 'cheek'. Over time, as the word evolved from Latin to Spanish, the meaning narrowed to specifically refer to the 'mouth' rather than the cheek area.

Some common Spanish words derived from the same root include 'bocado' (meaning 'mouthful' or 'bite'), 'bocadillo' (meaning 'sandwich'), and 'bocanada' (meaning 'puff' or 'mouthful'). All these words maintain a clear connection to the mouth and eating.

While English 'mouth' comes from a different root, there are some English words related to 'boca' through the Latin 'bucca'. For example, 'debouch' (meaning 'to emerge or exit from a narrow or confined space') comes from French 'déboucher', ultimately from the same Latin root. The technical term 'buccal', meaning 'relating to the cheek or mouth' in medical contexts, also comes from Latin 'bucca'.