A circumfix or circumflection is an affix, a morpheme which is placed around another morpheme. Circumfixes contrast with prefixes, attached to the beginnings of words; postfixes, that are attached at the end; and infixes, inserted in the middle. See also epenthesis.
For instance, in Hebrew magdelet "magnifier", the root is gdl "big" (in the H-stem hagdel "to enlarge") and the circumfix is m---et. Similarly, in classical French, negation is achieved by the circumfix ne . . . pas which is placed around either the chief verb or the auxiliary verb of a verb phrase. Circumfixes are extremely common in Bahasa Indonesia.
Probably the only circumfixes in English are: "en-...-en" and "em-...-en" in "enlighten" and "embolden". One cannot say "enlight" (although "lighten" is correct); "embold" and "bolden" are both incorrect.