Definitions of alumni on the Web:

• An alumnus (pl. alumni) according to the American Heritage Dictionary is "a male graduate or former student of a school, college, or university. ...
  en.wikipedia.org/wiki/Alumni

• An alumnus or an alumna
  en.wiktionary.org/wiki/alumni

• alumnus - a person who has received a degree from a school (high school or college or university)
  wordnetweb.princeton.edu/perl/webwn

• alumnus - a male pupil or student; a male graduate; a student; a graduate
  en.wiktionary.org/wiki/alumnus

• These Latin words refer to graduates of a college or university.
  www.usaeducationguides.com/guidance/articles/080707-glossary-academic-terms.jsp

• Any student who has graduated from a University is considered part of the Alumni network (or ‘Alumnus’ singular). ...
  www.latrobe.edu.au/transition/uni-speak.html

• graduates of an institution of higher education.
  www1.athabascau.ca/hr/recruit_orient/new_staff/general_glossary.html

• alumnus - An initiated member of a fraternity who has graduated from college.
  www.tkeclarion.net/terms.html

• Students who have graduated from a particular institution. Many colleges and universities provide continuing services to alumni. Alumni associations often support the school through fund-raising, alumni magazines, and volunteer activities.
  oregonone.org/glossary.htm

• a forum of all past graduates, academic staff, past and present Council members and other qualified members.
  www.studentservices.qut.edu.au/info/facts/glossary/ad.jsp

• These are graduates of the institution. The institution is their alma mater. Alumni support their alma mater by providing information to prospective students and current students and by making financial contributions to the institution. ...
  www.tulsacc.edu/page.asp

• Graduates, in the plural. ARTICULATION AGREEMENT A formal agreement between Three Rivers Community College and a four-year college or university ...
  www.trcc.commnet.edu/Gen_Info/Catalog/glossary.htm

• A member who is no longer a full-time student or has graduated.
  www2.uwsuper.edu/phisigmasigma/vocabulary.htm

• Combined group of men and women who have attended a college or university. "Alumnus" is the masculine singular; "alumni" is masculine plural; "alumna," femine singular; and "alumnae," feminine plural. These words are from Latin, their root meaning foster child or pupil.
  www.nuphi.com/terms.htm

• Former Pupils of The King's School
  www.thekingsschool.co.uk/newsinfo/jargonbuster.php