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al- (1)

http://www.etymonline.com/word/*al-
Proto-Indo-European root meaning "beyond."

It forms all or part of: adulteration; adultery;
alias; alibi; alien; alienate; alienation;
allegory;
allele; allergy;
allo-; allopathy; allotropy;
Alsace;
alter; altercation; alternate; alternative; altruism; eldritch; else; hidalgo;
inter alia; other; outrage; outrageous; outre;
parallax; parallel;
subaltern;
synallagmatic;
ulterior; ultimate; ultra-.

It is the hypothetical source of/evidence for its existence is provided by:
Sanskrit anya "other, different," arana- "foreign;"
Avestan anya-,
Armenian ail "another;"
Greek allos "other, different, strange;"
Latin alius "another, other, different," alter "the other (of two)," ultra "beyond, on the other side;"
Gothic aljis "other,"
Old English elles "otherwise, else,"
German ander "other."