In a tat-puruṣa samāsa the first member preserves its original accent when it is a word - 1. meaning 'a resemblance' or 2. an Instrumental or 3. a Locative or 4. a word with which the second member is compared or 5. an indeclinable or 6. an Accusative or 7. a Future Passive Participle,
Thus (1) तुल्यश्वेतः, तुल्यलोहित, तुल्यमहान्, सदृक्च्छ्वेतः, सदृग्लोहितः सदृग्महान् ॥ These are Karmadharaya compounds formed under 2.1.68: and तुल्य being formed by यत् is acutely accented on the first 6.1.216. The word सदृक् is formed by क्विन् 3.2.60 Vartika)), and has acute on the final 6.1.197 and 6.2.139. So also सदृशश्वेतः सदृशलोहितः, सदृशमहान् ॥ The word सदृश is formed by कञ् added to दृश्, and by (VI. I. 197) the accent falls on दृ 6.2.139. (2) When the first member is in the Instrumental case, as :- शंकुलया खण्डः = शंकुलाखण्डः, so also किरिकाणः (II. I. 30) शंकुला is derived from शंकु + ला ॥ To the root ला is added the affix क with the force of घञ्, and thus the noun ला is udatta, or the whole word शंकुला is a word formed by क affix and hence 6.1.165 applies and is final-acute. किरिः is formed by the Unadi affix इ to कृ (Unadi IV. 143), and it being treated as a कित् (Unadi. IV. 142) has udatta on the final.
(3) When the first member is a word in the Locative case, as :- अक्षेषु शौण्डः = अक्षशौण्डः, so also पानशौण्डः ॥ The word अक्ष is formed by the affix त added to अश् (Un III. 65), and is final acute 3.1.3. The word पान is formed by ल्यूट् affix added to पा, and is acute on the first 6.1.193 owing to the लित् accent. (4) When the first member is a word with which the second member is compared, as:- शस्त्रीश्यामा, कुमुदश्येनी, हंसगद्गदा, न्यग्रोधपरिमण्डला, दूर्वाकाण्डश्यामा, शरकाण्डगौरी ॥ These compounds are formed by 2.1.55. शस्त्री is formed by ङीप् and is final-acute; कुमुद is formed by क affix (कौ मोदते = कुमुद) see 3.2.5. Vartika)): and is acutely accented on the first, or by Phit sutra II. 3 it has acute on the first. हंस is formed by the Unadi affix स added to हन् (Unadi III. 62), and is finally accented 3.1.3. न्यग्रोहति = न्यग्रोधः formed by अच् 3.1.134, and ह is irregularly changed into ध as Panini himself uses this form 7.3.5: and it is accented in the middle. The words दूर्वाकाण्ड, शरकाण्ड are Genitive Tatpurusha, and their second member has accent on the first syllable 6.2.135, (5) When the first member is an Indeclinable, as, अब्राह्मणः, अवृषलः, कुब्राह्मणः, कुवृषलः ॥ निष्कौशाम्बिः, निर्वाराणासिः, अतिखट्वः, अतिमालः ॥ All these Indeclinable compounds have udatta on the first, they are formed by 2.2.5 &c.
Vart:- In cases of Indeclinable compounds, the rule applies only to those which are formed by the negative Particle अ, by कु, and by Particles (nipata). Though नञ्, is one of the Nipatas, its separate mention indicates that नञ्-accent debars even the subsequent कृत्-accent as अकरणिः ॥ Therefore, it does not apply here स्नात्वाकालकः which has acute on the final and belongs to Mayuravyansakadi class.
(6) When the first member as in the accusative case, as:- मुहूर्त्तसुखम्, मुहूर्त्तरमणीयम्, सर्वरात्रकल्याणी, सर्वरात्रशोभना ॥ They are formed by 2.1.29. मुहूर्त्त belongs to पृषोदरादि class and is acutely accented on the last. सर्वरात्र is formed by the samasanta affix अच् and is finally accented.
(7) When the first member is a Kritya-formed word, as, भोज्यलवणम्, भोज्योष्णम्, पानीयशीतम्, हरणीयचूर्णम् 2.1.68. भोज्य is formed by ण्यत् and has svarita_ on the final : पानीय and हरणीय are formed by अनीयर् and are accented on the penultimate 6.1.185 and 6.1.217 i. e. on ई ॥,