Uath

Uath, Old Irish Úath, hÚath, is the sixth letter of the Ogham alphabet, ᚆ, transcribed $⟨ʜ⟩$ in manuscript tradition, but unattested in actual inscriptions. The kenning "a meet of hounds is huath" identifies the name as úath "horror, fear", although the Auraicept glosses "white-thorn":
 * comdal cuan huath (.i. sce L. om); no ar is uathmar hi ara deilghibh "a meet of hounds is huath (i.e. white-thorn); or because it is formidable (uathmar) for its thorns."

The original etymology of the name, and the letter's value, are, however, unclear. McManus (1986) suggested a value /y/ (i.e. the semivowel [j]). Peter Schrijver suggested that if úath "fear" is cognate with Latin pavere, a trace of PIE *p might have survived into Primitive Irish, but there is no independent evidence for this.

Bríatharogam
In the medieval kennings, called Bríatharogam or Word Ogham the verses associated with Úath are:

condál cúan - "assembly of packs of hounds"	 in the Word Ogham of Morann mic Moín

bánad gnúise - "blanching of faces" in the Word Ogham of Mac ind Óc

ansam aidche - "most difficult at night"" in the Word Ogham of Culainn.