LOST LETTERS

What are those letters that I need, The crossword to complete? It seems to happen every day, And I must admit defeat. The wording of the clue is vague, ‘Unguis’ is what it says, Thesaurus and the dictionary, On it cast no rays. I do not want to give up now, On such a little thing, If I can crack this silly word, You’ll see me dance and sing. Wikipedia knows more than me, I’d go and ask the man, But he lives in a computer, And I’ve never been a fan. With 26 to choose from, It leaves me with such sorrow, I’ll wait until the answer comes, And fill it in tomorrow. Paul Scrivener, Bedford.