The American Heritage® Dictionary of the English Language: Fourth Edition. 2000.
Appendix I
Indo-European Roots
ENTRY:
ak-
DEFINITION:
Sharp. Oldest form *2e-, colored to *2a-, becoming *a- in satem languages and *ak- in centum languages. Derivatives include acute, hammer, heaven, eager1, vinegar, acid, and oxygen. 1. Suffixed form *ak-y-.a.edge; selvage, from Old English ecg, sharp side, from Germanic *agj;b.egg2, from Old Norse eggja, to incite, goad, from Germanic *agjan.2. Suffixed form *ak-u-.a.ear2, from Old English æhher,ar, spike, ear of grain, from Germanic *ahuz-;b.acicula, acuity, aculeate, acumen, acupuncture, acute, aglet, ague, eglantine, from Latin acus, needle; c.acerose, from Latin acus, chaff. 3. Suffixed form *ak-i-.acidanthera, from Greek akis, needle. 4. Suffixed form *ak-men-, stone, sharp stone used as a tool, with metathetic variant *ka-men-, with variants: a.*ka-mer-.hammer, from Old English hamor, hammer, from Germanic *hamaraz;b.*ke-men- (probable variant). heaven, from Old English heofon,hefn, heaven, from Germanic *hibin-, “the stony vault of heaven,” dissimilated form of *himin-.5. Suffixed form *ak-on-, independently created in: a.awn, from Old Norse ögn, ear of grain, and Old English agen, ear of grain, from Germanic *agan; and b.paragon, from Greek akon, whetstone. 6. Suffixed lengthened form *k-ri-.acerate, acrid, acrimony, eager1; carvacrol, vinegar, from Latin cer, sharp, bitter. 7. Suffixed form *ak-ri-bhwo-.acerbic, exacerbate, from Latin acerbus, bitter, sharp, tart. 8. Suffixed (stative) form *ak--.acid, from Latin acre, to be sharp. 9. Suffixed form *ak-to-.acetabulum, acetic, acetum; ester, from Latin actum, vinegar. 10. Suffixed form *ak-m-.acme, acne, from Greek akm, point. 11. Suffixed form *ak-ro-. acro-; acrobat, acromion, from Greek akros, topmost. 12. O-grade form *ok- (from earlier *ok-) in suffixed form *ok-ri-.mediocre, from Latin ocris, rugged mountain. 13. Suffixed o-grade form *ok-su-.amphioxus, oxalis, oxygen, oxytone, oxyuriasis, paroxysm, from Greek oxus, sharp, sour. (Pokorny 2. a- 18, 3. em- 556.)
2e
-, colored to *
-. a. edge; selvage, from Old English ecg, sharp side, from Germanic *agj
; b. egg2, from Old Norse eggja, to incite, goad, from Germanic *agjan. 2. Suffixed form *ak-u-. a. ear2, from Old English æhher, 
ar, spike, ear of grain, from Germanic *ahuz-; b. acicula, acuity, aculeate, acumen, acupuncture, acute, aglet, ague, eglantine, from Latin acus, needle; c. acerose, from Latin acus, chaff. 3. Suffixed form *ak-i-. acidanthera, from Greek akis, needle. 4. Suffixed form *ak-men-, stone, sharp stone used as a tool, with metathetic variant *ka-men-, with variants: a. *ka-mer-. hammer, from Old English hamor, hammer, from Germanic *hamaraz; b. *ke-men- (probable variant). heaven, from Old English heofon, hefn, heaven, from Germanic *hibin-, “the stony vault of heaven,” dissimilated form of *himin-. 5. Suffixed form *ak-on
