The Spanish adverb 'seguramente' (meaning 'surely') comes from combining the adjective 'seguro' ('safe, secure') with the adverbial suffix '-mente' (meaning 'in a manner of'). The suffix '-mente' itself comes from the Latin word 'mens' meaning 'mind'.

Going further back, 'seguro' comes from Latin 'securus', which was formed by combining the prefix 'se-' ('apart') with 'cura' ('care, concern'). So 'securus' literally meant 'free from care' or 'without worry', which evolved to mean 'safe, secure' in both Latin and its Spanish descendant.

The most obvious related Spanish word is the simpler and more common 'seguro', meaning 'safe' or 'secure'. You might hear this in phrases like 'estar seguro' (to be sure) or '¿estás seguro?' (are you sure?). There's also the noun 'seguridad' meaning 'security' or 'safety'.

The English words 'secure' and 'sure' are cousins of 'seguramente', as they also come from Latin 'securus'. You can see how the meanings are all related to the idea of being free from worry or doubt. The English word 'surety' and 'assure' are also part of this family. Even 'insurance' contains this same root - it's about making something secure against risk!