Vachaka Shakti is the inherent potency of a word to communicate a referent. The essential nature of an articulated word lies in its power to communicate a meaning. This power is referred to by the word shakti (potency).
This communication is known as abhidhanam, according to early Mimamsakas. A relation between a word and its meaning may be either direct or indirect. The direct relationship is termed by Mammata (11th century CE) as sanketa. If the relationship is abiding and direct, it is called Vachaka Shakti.
The Mimamsakas hold this power as a natural relationship with the object which the particular word signifies, and is eternal, since they accept the Vedic knowledge texts to be eternal and unchanging. They are called advocates of Nityasaktivada (doctrine of word power as unchanging. The logicians hold that the relation is conventional and is established by the will of Brahman. For them, will of Brahman is Shakti. What is conveyed through Shakti is Shakyarhta or abhidheya or mukhyartha (primary meaning). The word is called Shakta (powerful), vachaka or abhidhana (expression). Opposed to this power is lakshana (secondary meaning).
This expressive power again is said to have a three-fold convention of rudha, yaugika (etymological), and yogarudha (conventional while etymologically dissoluble). Conventional is that word which is not analyzed into its parts for an understanding of the word, like kamalam (lotus), whereas ambuja means lotus in its capacity of being produced in water (ambu – water; ja – born), hence, the etymology. Pankaja means produced in mire, but by convention is restricted to the lotus only, hence yogarudha. Some people consider polynomials as words with many expressive powers. Discussions as to the meaning conveyed by a word have been held from very early days, and different bitterly among themselves. Vajapyayana holds jati (genus) to be its meaning, while Vyadi held vyakti (individual) to be the meaning. Many people subscribe to the former viewpoint, while grammarians concede with viewpoints, depending on the context.