同窓である
graduated from the same school; went to the same school
〈同期〉 《主に米国で用いられる》 was in school 《with》; 《主に英国で用いられる》 was at school 《with》; were at the same school.
〈組織〉 《主に米国で用いられる》 an alumni association; 《主に英国で用いられる》 an old boys' [girls'] association
〈会合〉 a class reunion (同年次の); 《主に米国で用いられる》 an alumni meeting
〈卒業生〉 a graduate; an old boy; 《主に米国で用いられる》 an alumnus 《《複数形》 ‐ni》 (男); 《主に米国で用いられる》 an alumna 《《複数形》 ‐nae》 (女)