The Spanish word 'malecón' comes from the Latin word 'murex', which had two related meanings: it referred to both a spiny sea snail and a pointed rock. Through Vulgar Latin, the word evolved into '*murico' and its accusative form '*muriconem', maintaining the meaning of 'pointed rock'. Over time, as the word made its way into Spanish as 'malecón', its meaning became more specific, referring to a seawall or breakwater - a structure built along the coast to protect against waves and erosion. This semantic evolution makes sense considering these structures were often built with or upon pointed rocks along the shoreline.

While 'malecón' is a fairly unique word in Spanish without many common related words, it's worth noting that it's a very common feature in Spanish-speaking coastal cities, where these seawalls often serve as popular waterfront promenades.

Interestingly, English preserved the marine snail meaning of the Latin 'murex' rather than the rocky meaning that led to Spanish 'malecón'. The word 'murex' exists in English as a scientific term referring to a genus of predatory sea snails. These mollusks were historically important as the source of Tyrian purple dye, highly valued in ancient times.