Welcome to Mi Yodeya. It looks like the word is not "monen" but M'onein. It is a category of forbidden practice in Deuteronomy 18:10. Rashi there brings two opinions:
מעונן. רַבִּי עֲקִיבָא אוֹמֵר אֵלּוּ נוֹתְנֵי עוֹנוֹת – שֶׁאוֹמְרִים עוֹנָה פְּלוֹנִית יָפָה לְהַתְחִיל, וַחֲכָמִים אוֹמְרִים אֵלּוּ אוֹחֲזֵי הָעֵינַיִם:
מעונן — Rabbi Akiba said, Such are people who assign times (עונות plural of עונה “period”, “time”) — who say, “This time is auspicious to begin some work”; the Sages, however, say, It refers to those “who hold your eyes under control” (who delude by optical deception; they connect מעונן with עין “eye”) (Sifrei Devarim 171:9).
The Wikipedia entry is probably going with the opinion of R' Akiva, and it refers to those who use astrology to find favorable times for different activities.