I read someone mentioning 蔑 as a negation word in classical Chinese, but unfortunately without explaining how it works or an example sentence. So I looked it up in my dictionary and it only showed me the meaning as a verb for denouncing s.o.
Here's a good English definition and explanation with an example sentence to get you started:
A Students Dictionary of Classical and Medieval Chinese
2 negative particle of the perfective: had not, have not, will have not; similar to 末 mò and often accompanied by perfective-final 矣 yǐ; mostly found in Zuozhuan 左傳 and Guoyu 國語, later mainly for archaic effect; e.g. 寧事齊楚, 有亡而已, 蔑從晉矣 níngshì Qí Chǔ, yǒu wáng éryǐ, miècóng Jìn yǐ, Better to serve Qi and Qi, lest we simply perish, and [better] not to have followed Jin.
3 not to have, lack; there are no…
Next you can have a look at these dictionary samples to get a better grip of how it works (some of the definitions are the same, but they use different sources):
◆ <副> 無、沒有。
Hanyu Da Cidian
《诗·大雅·板》 喪亂蔑資, 曾莫惠我師。
毛 传 蔑, 無。資, 財也。
《史记·孔子世家》 夫子循循然善誘人, 雖欲從之, 蔑由也已。
《新唐书·突厥传赞》 自《詩》《書》以來, 伐暴取亂, 蔑如帝神且速也。
明 胡应麟 《少室山房笔丛·华阳博议上》 即小學一端, 門逕十數, 古今博洽, 蔑能相兼。
Gu Hanyu Cidian
[Miè 蔑 is a] form corresponding to wú 無 ‘not have’ in the same way that [...] wù 勿 corresponds to wú 毋 ‘do not.’
And here's what Pulleyblank writes about the relation of 勿 and 毋:
That is, the ancestral forms of the two graphs on the oracle bones appear to have an aspectual distinction, while in the Warring States period there is reason to think that the final -t of wù 勿 may have been interpreted as the incorporated object pronoun zhī 之.
That is, he writes that in 勿 in the Warring States period was interpreted to be the same as 毋之. The “aspectual distinction” from the earlier period seems to be the distinction between an unmarked sentence and a sentence ending with 矣, which is analysed by Pulleyblank as expressing the perfect aspect.
And here is an example sentence:
If I expel the ruler of Jìn and you bring in Chóng'ĕr, everything will be successful. (Zuŏ Xī 10/fù. Literally: ‘there will be no not succeeding’)
From XinHua dictionary:
1. 目受伤而不明。eye injury so can't see or see clearly
2. 无，没有：蔑以复加。none, nothing: can't be more...
3. 小：蔑视。轻蔑。little, down: contempt
5. 涂染：诬蔑。污蔑。 drawing (bad things): vilification
In ancient Chinese, 蔑 was used as "none, nothing or to eliminate".
But now we use it as "little or down" (like 蔑视, 轻蔑) and "drawing (bad things to somebody)" (like 污蔑).