Let us find words with a letter, be it a vowel or a consonant, repeat itself in a word, THE CONDITION IS THAT THE REPEATING LETTER SHOULD NOT APPEAR CONSECUTIVELY. eg., purple - letter p is repeating, but not consecutively. So allowed. O.K. consonant - letters o & n are repeating, but not consecutively. O.K. letter - discarded because the letter t appears consecutively, even though the letter e appears at different places. appear - discarded because the letter p appears consecutively. error - discarded because the letter r appears consecutively.