the adverb 'surely' originates from middle english 'surly', which was formed by combining the adjective 'sure' with the adverbial suffix '-ly'. the adjective 'sure' itself descends from old english 'sīcur', meaning 'secure, safe', which was borrowed from old french 'seür'. this old french term ultimately traces back to latin 'sēcūrus', a compound of 'sē-' (meaning 'without') and 'cūra' (meaning 'care'), thus literally 'without care' or 'free from anxiety'. over time, the sense evolved from a state of safety to one of certainty, and the addition of the '-ly' suffix created the adverb expressing manner or degree of certainty.

the word is an adverb formed by adding the suffix '-ly' to the adjective 'sure'. it is not segmented further as 'sure' itself is a simplex word of old english origin.