B.G 2.26
अथ चैनं नित्यजातं नित्यं वा मन्यसे मृतम्। तथापि त्वं महाबाहो नैनं शोचितुमर्हसि ॥२-२६॥
O mighty armed, even if you regard the being as inevitably born, and inevitably dying, it is not right for you to grieve.
Gīta Tātparya 2.26
The word 'nityam' in this verse means 'inevitable' based on context and dictionary.
तिष्ठतु तावत् अयं विस्तारः। यावन्मोक्षं जीवस्य जन्ममरणे स्वयमेव मन्यसे ननु नियमेन। तथापि तावन्मात्रेणापि ज्ञानेन शोचितुं नार्हसि।
Despite the explanations provided so far, you must still wait to get liberated. In the meantime, birth and death are both subject to the law and unavoidable. With this minimal knowledge, it is clear that grieving is not worth it.
"नित्यं सनातनं प्रोक्तं नित्यं नियतमेव च"। इति शब्दनिर्णये।
'The word 'nitya'means that which is eternal. It also means that which cannot be avoided" - states "shabdanirnaya" dictionary.
अत्र तु नियतम्। "जातस्य हि ध्रुवः" इति प्रकाशनात् ॥२६॥
The word 'nitya' should be interpreted as that which is inevitable. Because is the next verse "jātasya hi dhruvaḥ", a similar meaning is expressed using the word "dhruvaḥ".