तत्पुरुषः समानाधिकरणः कर्मधारयः

A तत्-पुरुष compound, the case of each member is the same, is called कर्मधारय or Appositional Determinative compound.
"Karmadharaya or Appositional Determinative compounds form a sub-division of the determinative compounds (Tat-purusha). In them the first portion stands as the predicate of the second portion, such as in black-beetle, sky-blue." (Max Muller).

The compounds like नीलोत्पलं 'the blue lotus', परमात्मा 'the supreme spirit' &c., are examples of karmadharaya compounds. "The component words, if dissolved, would stand in the same case, (samanadhikarana), whereas in other Tat-purushas, the preceding word is governed by the last."

As, परमराज्यम्, is a karmadharaya compound meaning "the best Government." Had it not been a karmadharaya compound, the udatta accent would have fallen on the syllable रा by rule 6.2.130 \[1\] ,(the word राज्यम् has udatta on the first syllable in Tat-purusha compounds, except in karmadharaya).

Similarly पाचिका + वृन्दारिका = पाचकवृन्दारिका (6.3.42 \[2\] ,the feminine adjective is changed into masculine in the karmadharaya).

Each member of a compound may have the same case, but if it is not a Tat-purusha compound, it won't be karmadharaya. As पाचिका + भार्या = पाचिकाभार्याः. 'He who has a wife for a cook.' This is an example of a Bahuvrihi compound, and therefore the word पचिका retains its gender sign.

A compound may be a Tat-purusha, but if its component parts do not refer to the same thing and are not in the same case, it won't be karmadharaya:- ब्रा॒ह्म॒ण॒ राज्य॑म् Brahmana rajyam, 'a Brahmana kingdom.' Here राज्यम् gets udatta on the first syllable by the rule already mentioned 6.2.130.

## Footnotes
- [1] - अकर्मधारये राज्यम् ॥
- [2] — पुंवत्कर्मधारयजातीयदेशीयेषु ॥