Solutions Formal letter has 4 entries with similar clues

• 4-letter words
• alfafirst nato phonetic letter, which sounds like the first greek letter
• 9-letter words
• dear-sirsFormal opening in a letter to a firm or organisation
• diacriticA sign written above or below a letter to indicate a difference in pronunciation from the same letter when unmarked
• 11-letter words
• haplographyInadvertent omission of repeated letters or letters in writing