Since all common vowels (a, e, i, o) have been guessed and aren't in the word, this might be a word with 'y' as its only vowel. "Rhythm" is a strong possibility - it's 6 letters, starts with 'r', has 't' in the 4th position, and contains no common vowels. Guessing 'h' makes sense as it appears twice in "rhythm", potentially revealing multiple letters at once.