नञ्

The negative word नञ् is compounded with a case-inflected word with which it is in construction, and the compound is तत्-पुरुष।
As न ब्राह्मणः = अब्राह्मणः 'who is not a Brahmana,' (though a man). The म् of न is elided by 6.3.73:

Vart: - The न् of न is also elided even when the second member is a verb, provided that censure is implied as अपचसि त्वं जाल्म 'thou cookest not O knave.'

The word नञ् has six senses: (1) सादृश्य 'likeness or resemblance'; as अब्राह्मणः 'one like a Brahmana and wearing the sacred thread &c., but not a Brahmana, but a Kshatriya or a Vaisya.' (2) अभाव 'absence,' 'negation,' 'want,' or 'privation,' as अज्ञान 'absence of knowledge.' (3) भेदः 'difference' or 'distinction,' as अपटः 'not a cloth, but something different from or other than a cloth'. (4) अल्पता 'smallness,' 'diminution' used as diminutive particle, as अनुदरा' having a slender waist.' (5) अप्राशस्त्य 'badness,' 'unfitness,' having a depreciative sense, as अकाल 'wrong or improper time.' (6) विरोध 'opposition,' 'contrariety,' as अनीतिः 'opposite of morality,' 'immorality.'