Abarim Publications' online Biblical Greek Dictionary
αχος
The noun αχος (achos) means pain or distress (hence our word "ache"). It stems from the same Proto-Indo-European root "heg-", meaning to be upset or afraid, as the English verb to ail. It occurs frequently in Homer, and always as a state of mind. Apart from two derived names, this word does not occur in the New Testament, but note the accidental similarity with the noun αχυρον (achuron), chaff or grinding residue.
αχθος
The noun αχθος (achthos) means burden or load (literally, of camels and such) or grief or sorrow. It is thought to stem from a poorly attested PIE root "hedg-", to squeeze or oppress, but it's obviously similar to the previous, as native speakers of Greek would have surely noticed. This noun does not occur independently in the Bible, but from it comes:
- Together with the adverb αγαν (agan), very much (an otherwise unused variant of μεγας, megas, great or large): the verb αγανακτεω (aganakteo), meaning to be greatly irritated or vexed. It's actually not certain whether this verb comes from αχθος (achthos), burden, and may very well also have something to do with the adjective ακτεοσ (akteos), to-be-drawn or to-be-lead, from the verb αγω (ago), meaning to lead. But whatever its pedigree, this verb is used 7 times, see full concordance, and from it in turn comes:
- The noun αγανακτησις (aganaktesis), meaning great irritation, vexation or indignation (2 Corinthians 7:11 only).