(uath, the whitethorn tree), an auxiliary letter in the Irish alphabet, used to express aspiration, to prevent hiatus, etc.; in modern Irish it is sometimes used instead of a dot over a letter to represent aspiration, and when Irish is written in Roman characters it is very commonly so used; it is written after the letter to be aspirated, thus, tighe; h- is prefixed by the article to all plural nouns beginning with a vowel, except in the genitive case, when it prefixes n-; h- is prefixed by the possessive prn., a, her, to nouns beginning with a vowel; h- is also often prefixed for euphony to the second of two words, one ending and the other beginning with a vowel.