This is the 188th most frequent Marathi word.
कध
The Marathi word "कध" means "when" in English.
In this sentence, 'कध' is part of 'कधनाही', used as an adverb to indicate 'never' (negative implication of ever).
तू कधनाही मला फोन करत नाहीस.
You never call me.
Here, 'कधी' is used as an interrogative pronoun to refer to 'whenever/in the future'. It implies time unspecific.
कधी वेळ मिळाल्यावर मला भेट.
Meet me whenever you get time.
In this case, 'कधीतरी' signifies 'someday/sometime'. It refers to an indefinite time in the future.