נַחַס, נַאַחַס

Slang is the most frequently evolving part of the language, and therefore it's enough to stay away for just couple of years and you start to lose track of it. Somebody brought me this word as mentioned in Hebrew newspaper, in a context of "bad luck". I googled for this word and found the following:

Slang: worse, bad luck סְלַנְג: רַע, גְּרוּעַ; רַע מַזָּל.
What a bad luck! I've broken my hand a day before field trip. אֵיזֶה מַזָּל נַחַס! יוֹם לִפְנֵי הַטִּיוּל שָׁבַרְתִּי אֶת הַיָּד.
Origin:
From Arabic: نَحْس bad luck, bringing bad luck		 מָקוֹר:
מֵעֲרָבִית: نَحْس - מַזָּל רַע, שֶׁמֵבִיא צָרָה.
Synonyms:
מַעֲפָן - have no idea what it means, and this might be another point to investigate.		 מִלִּים נִרְדָּפוֹת:
מַעֲפָן

All the information is taken from here.

The interesting part is, that if somebody is using the word "נַחַת" in its Yiddish pronunciation (like many American Jews are used to say), it would sound "נַחַס" (naches) - almost like this "נַאַחַס" thingie; that's while the meaning of נַחַת is most positive and the נַאַחַס is defintely negative. So, do not confuse! :)