As ' is feminine, the form ' might be expected, since a feminine noun causes initial consonant lenition in a following adjective, and indeed the everyday modern Gaelic for a normal 'black knife' is "". However, the term for the ceremonial knife is a set-phrase containing a fossilized historical form. In older Gaelic, a system of blocked lenition meant that lenition did not occur when the adjective started with a consonant of the same group as the final consonant of the noun, and n and d are both dental in Gaelic.