The term 'LETTER FOR CYNEWULF' can be solved by the word 'RUNE', which is a four-letter word. Runes are an ancient form of writing used by Germanic and Scandinavian peoples, and were used for a variety of purposes, including communication, divination, and magical or religious rituals. Runes were also used to write letters, and it is likely that the term 'LETTER FOR CYNEWULF' is referring to a letter written in runes.