mid-15c., menglen, transitive, "mix, blend, form a combination of, bring (something and something else) together," frequentative of Middle English myngen "to mix," from Old English mengan (related to second element in among), from Proto-Germanic *mangjan "to knead together" (source also of Old Saxon mengian, Old Norse menga, Old Frisian mendza, German mengen), from a nasalized form of PIE root *mag- "to knead, fashion, fit."
The formation may have been suggested by cognate Middle Dutch mengelen. Intransitive sense of "to be or become joined, combined, or mixed" is by 1520s. Of persons, "enter into intimate relation, join with others, be sociable," from c. 1600. Related: Mingled; mingling; minglement.