The Spanish word 'muerto' meaning 'dead' comes from the Latin word 'mortuus' with the same meaning. It's also closely related to the Latin verb 'mori' meaning 'to die', which evolved through Vulgar Latin 'morire' into the modern Spanish verb 'morir' ('to die'). The change from Latin 'mortuus' to Spanish 'muerto' shows a common sound change where the Latin 'o' became the Spanish 'ue' diphthong.

Some common related Spanish words include the verb 'morir' (to die), 'muerte' (death), and 'mortal' (mortal). These all share the same Latin root and form a family of words related to death and dying. The adjective 'muerto' is actually the past participle of 'morir', just like in English we have 'die' and its past participle 'dead'.

English speakers might recognize this root in words like 'mortal' (capable of dying), 'mortality' (death rate), 'mortuary' (a place for the dead), and 'mortician' (one who handles the dead). Even the word 'murder' is distantly related, all coming from the same ancient root meaning death or dying. The Latin root 'mort-' has been very productive in English, especially in formal or technical vocabulary.