Why is the ninth month called September?
word-forming element meaning "both, on both sides," from Latin ambi- "around, round about," from PIE *ambhi "around" (cf. Greek amphi "round about," Sanskrit abhitah "on both sides," Avestan aibi, Old English ymbe, German um, Gaulish ambi-, Old Irish imb- "round about, about," Old Church Slavonic oba, Lithuanian abu "both"). The PIE root probably is an ablative plural of *ant-bhi "from both sides," from *ant- "front, forehead" (see ante).
ambi- or ambo-