The Spanish word 'laguna' comes from the Latin word 'lacūna', which meant 'pool' or 'pond'. The evolution from Latin to Spanish shows a typical sound change where the 'c' (pronounced like 'k') softened to a 'g' sound, a common phenomenon in the development of Spanish from Latin. The meaning has remained quite stable, as 'laguna' in Spanish refers to a lagoon or lake, maintaining the basic concept of a body of water.

A closely related Spanish word is 'lago' (lake), which comes from the Latin 'lacus'. Both 'laguna' and 'lago' share their aquatic origins and are often used somewhat interchangeably in modern Spanish, though 'laguna' typically refers to a smaller body of water or one that might be more shallow or coastal.

English speakers might recognize the connection to the word 'lagoon', which is actually borrowed from Italian 'laguna' (related to Spanish 'laguna'). Another interesting English cognate is 'lacuna', which comes directly from the same Latin word 'lacūna', though its meaning has shifted to refer to a gap or missing part in a text or knowledge - imagine a 'hole' or 'empty space' like a pool, but in a metaphorical sense.