A letter to Santa is a traditional Christmas activity for children, in which they write a letter to Santa Claus expressing their wishes for the holiday season. The four letter crossword solutions for the term 'letter to Santa' are 'NOTE', 'MISSIVE', 'EPISTLE', and 'LINE'. A NOTE is a short written message, while a MISSIVE is a longer, more formal letter. An EPISTLE is a formal letter, usually written in a literary style, and a LINE is a single sentence or phrase.