Aicme hUatha is the second group, named for uath, and its five letters are uath, dair, tinne, coll and cert, giving the sounds h, d, t, c and q. In the script these are cut as one to five strokes to the left of the stemline, or above it when the line is horizontal. The presence of a distinct letter for q, representing the Primitive Irish sound that later became c, is one of the pieces of internal evidence used to date the alphabet's design: it fits a stage of the language earlier than the surviving inscriptions themselves, which suggests the alphabet was devised somewhat before the earliest stones. Damian McManus's A Guide to Ogam (1991) is the standard modern treatment of these questions.
The name uath is itself disputed in a way beithe is not: the letter kennings in the medieval tradition connect it to Old Irish uath, fear or horror, while the Auraicept's separate arboreal gloss instead gives whitethorn or hawthorn, reconciled by later scribes through wordplay on uathmar, fearsome, since thorns were read as a fearsome tree. Damian McManus, in A Guide to Ogam (1991), judged the manuscript tradition's h sound value for the letter a likely later, cosmetic fix over a lost original consonant, tentatively proposing the sound /y/ instead, while treating the letter's true original name and value as genuinely unresolved rather than settled by either the fear or the hawthorn reading.
Sources A Guide to OgamDamian McManus with Auraicept na n-Eces: The Scholars' PrimerGeorge Calder (ed.)