The Spanish word 'seco' meaning 'dry' comes directly from the Latin word 'siccus', which meant 'dry' or 'without moisture'. The evolution from Latin to Spanish involved a typical sound change where the double 'cc' simplified to 'c', and the Latin ending '-us' was dropped, as happened with many Spanish words derived from Latin.

Some related Spanish words include 'secar' (to dry), 'sequía' (drought), and 'reseco' (very dry or parched). These words all share the same Latin root and form a family of words related to dryness or the absence of moisture.

While English 'dry' comes from a different root, we do have some technical English words from the same Latin source, such as 'desiccate' (to remove moisture) and 'desiccant' (a substance used to remove moisture). These words preserve the original 'sicc-' root from Latin 'siccus'.