Fortition

In articulatory phonetics, fortition, also known as strengthening, is a consonantal change that increases the degree of stricture. It is the opposite of the more common lenition. For example, a fricative or an approximant may become a stop (i.e. [v] becomes [b] or [r] becomes [d]). Although not as typical of sound change as lenition, fortition may occur in prominent positions, such as at the beginning of a word or stressed syllable; as an effect of reducing markedness; or due to morphological leveling.