kārma is irregularly formed from karman by the elision of the final an when the sense is 'accustomed to such occupation or prompt therein'.,
This is formed by ण affix 4.4.62. If this is the case, then by 6.4.144, the form कार्म is regularly evolved. The fact is, that ण् and अण् affixes, in the sense of tachchhilika are considered as one, and therefore 6.4.167, would have prevented the elision of the final अन् syllable. In fact this proves the existence of the folloving maxim :- ताच्छीलिके णेऽण् कृतानि भवन्ति ॥ \The same operations which are occasioned by the addition of the affix अण्, take place, whenever the affix ण is added in the sense of one accustomed to that.\ Thus though ङीप् is added, to अण् - formed words, it is also added to ण - formed words, in the feminine: as चौरी; तापसी &c. The ण taught in 5.2.101, and 3.1.140, is excepted. Why do we say, having the sense of accustomed to that? Observe कर्मणः इदम् = कार्मणम् ॥,