*al- (2) Look up *al- at Dictionary.com
Proto-Indo-European root meaning "to grow, nourish."

It forms all or part of: abolish; adolescent; adult; alderman; aliment; alimony; Alma; alma mater; alt (2) "high tone;" alti-; altimeter; altitude; alto; alumnus; auld; coalesce; elder (adj., n.1); eldest; Eldred; enhance; exalt; haught; haughty; hautboy; hawser; oboe; old; proletarian; proliferation; prolific; world.

It is the hypothetical source of/evidence for its existence is provided by: Greek aldaino "make grow, strengthen," althein, althainein "to get well;" Latin alere "to feed, nourish, suckle; bring up, increase," altus "high," literally "grown tall," almus "nurturing, nourishing," alumnus "fosterling, step-child;" Gothic alþeis, Dutch oud, German alt "old;" Gothic alan "to grow up," Old Norse ala "to nourish;" Old Irish alim "I nourish."