The American Heritage® Dictionary of the English Language: Fourth Edition. 2000.
Appendix I
Indo-European Roots
ENTRY:
al-1
DEFINITION:
Beyond. Oldest form probably *2el-, colored to *2al-. Derivatives include alarm, ultimate, else, alien, alibi, and parallel. 1. O-grade form *ol- (earlier *2ol-), “beyond.” a. Compound forms *ol-se-,*ol-so- (*so-, pronominal stem; see so-). alarm, alert, alfresco, alligator, El Niño, hoopla, lagniappe, langue d'oïl, lariat, voilà, from Latin ille (feminine illa, neuter illud), “yonder,” that, from Archaic Latin ollus;b. suffixed forms *ol-s,*ol-tero-.outré, ulterior, ultimate, ultra-, utterance2, from Latin uls,*ulter,ultr, beyond. 2. Suffixed form *al-tero-, “other of two.” a.alter, altercate, alternate, altruism; subaltern, from Latin alter, other, other of two; b.adulterate, adulterine, adultery, from Latin adulterre, to commit adultery with, pollute, probably from the phrase ad alterum, “(approaching) another (unlawfully)” (ad, to; see ad-); c. variant suffixed form *an-tero-, “other (of two).” other, from Old English ther, from Germanic *antharaz.3. Suffixed form *al-eno-.Aranyaka, from Sanskrit araa-, foreign. 4. Extended form *alyo-, “other of more than two.” a.else; eldritch, from Old English el-,elles, else, otherwise, from Germanic *aljaz (with adverbial suffix); b.alias, alien; alibi, aliquot, hidalgo, from Latin alius, other of more than two; c. allo-; allegory, allelomorph, allelopathy, morphallaxis, parallax, parallel, trophallaxis, from Greek allos, other. (Pokorny 1. al- 24, 2. an 37.)
2el-, colored to *
, beyond. 2. Suffixed form *al-tero-, “other of two.” a. alter, altercate, alternate, altruism; subaltern, from Latin alter, other, other of two; b. adulterate, adulterine, adultery, from Latin adulter
ther, from Germanic *antharaz. 3. Suffixed form *al-eno-. Aranyaka, from Sanskrit ara
a-, foreign. 4. Extended form *alyo-, “other of more than two.” a. else; eldritch, from Old English el-, elles, else, otherwise, from Germanic *aljaz (with adverbial suffix); b. alias, alien; alibi, aliquot, hidalgo, from Latin alius, other of more than two; c. allo-; allegory, allelomorph, allelopathy, morphallaxis, parallax, parallel, trophallaxis, from Greek allos, other. (Pokorny 1. al- 24, 2. an 37.) 
