The word udaṅka is anomalous when the sense of the root refers to subjects other than 'water'.,
The word is thus formed: उत् + अञ्च + घञ् = उदङ्कः 'a vessel'.
Would not the affix घञ् have come by sutra 3.3.121, why then this aphorism? This is made a separate aphorism in order to prohibit the application of the affix, where the word to be formed means 'water'.
Thus तैलोदङ्कः 'a leathern vessel for oil'.
Why do we say 'when not referring to 'water'? Observe उदकोदञ्चनः 'a bucket for drawing water' (उद् + अञ्च + ल्युट्).
Why do not we give the counter-example by adding the affix घ to the root उदञ्च्? Because the form evolved by applying घ, would be the same in every respect as that evolved by घञ्; even the accent would be the same. For by sutra 6.2.144, the udatta accent, in the case of घञ्, will fall on the final.,