mön-

Usage notes
The form taken by this prefix depends on the first syllable of the stem it attaches to:
 * if the first syllable begins with a vowel or consonant other than or  and its vowel is anything but.
 * if the first syllable begins with a vowel.
 * if the first syllable begins with a vowel or consonant other than and its vowel is.
 * if the first syllable begins with a consonant.
 * if the first syllable begins with two consonants, e.g. as a result of syllable reduction.