It is used as a single word. Compound adjectives with the -ed form are always hyphenated or spelled as one word. (Absent-minded is occasionally found as a single word without a hyphen.)
Yes! But as a hyphenated word, "no-one."Can you omit the hyphen? No -- it might not be recognized. Would you write, "Noone will recognized this." It looks like the word "noon" with an exta "o".While...