The Spanish word 'protestantismo' (Protestantism) has its roots in Latin. It comes from combining two Latin elements: 'pro-' meaning 'forward' or 'in favor of', and 'testari' meaning 'to testify'. These combined to form the Latin verb 'protestari', which meant 'to declare publicly'.

From this Latin verb, Spanish developed the word 'protestante' (Protestant), to which the suffix '-ismo' was added. The suffix '-ismo' is used in Spanish to form nouns indicating a doctrine or system of beliefs, similar to the English '-ism'.

Some related and simpler Spanish words include 'protestar' (to protest), 'protesta' (protest), and 'testigo' (witness). All these words share the common thread of public declaration or testimony. 'Testigo' particularly preserves the meaning of the Latin 'testari' (to testify), while 'protestar' maintains the sense of making a public declaration.

English speakers can easily relate this word to several familiar terms: 'Protestant', 'protest', 'testify', and 'testimony'. All these words share the same Latin roots. The connection between 'protest' and 'Protestant' comes from the original sense of making a public declaration, which is what Protestant reformers did when they protested against certain practices of the Catholic Church. The words 'testify' and 'testimony' preserve the meaning of the Latin 'testari', showing how the concept of bearing witness or making declarations has remained consistent across languages.