"to ache, suffer pain," from P.Gmc. *akanan,
perhaps from a PIE base *ag-es-
"fault, guilt," represented also in Skt. and Gk., perhaps imitative of groaning. The noun is M.E. æche,
from O.E. æce,
from P.Gmc. *akiz.
The verb was pronounced "ake," the noun "ache" (by i-mutation,
as in speak-speech
) but while the noun changed pronunciation to conform to the verb, the spelling of both was changed to ache
c.1700 on a false assumption of a Gk. origin (Gk. akhos
"pain, distress"). Achy
(adj.) first attested 1875 in George Eliot's letters.