The dvanda and tat-puruṣa compound ending with the words rātra and ahna are spoken of in masculine.,
These words refer to krit and Samasanta affixes. Thus the word रात्र is formed by रात्रि + अच् 5.4.87 अह्न is formed by 5.4.88 and अह by 5.4.91. The general rule 2.4.26 also does not apply here.
द्विरात्रः, त्रिरात्रः 'A space of two or three nights' पूर्वाह्नः, अपराह्नः, मध्याह्नः 'the forenoon, the afternoon and noon', द्वहः 'two days' त्र्यहः, 'three days.'
Vart:- The words अनुवाक &c., are masculine, as अनुवाकः, शंयुवाकः, सूक्तवाकः &c.,