Ache
Old English æce (noun), acan (verb). In Middle English and early modern English the noun was spelled atche and rhymed with ‘batch’ and the verb was spelled and pronounced as it is today. The noun began to be pronounced like the verb around 1700. The modern spelling is largely due to Dr Johnson, who mistakenly assumed its derivation to be from Greek akhos ‘pain’.
wiktionary
From Middle English aken(verb), and ache(noun), from Old English acan(verb) (from Proto-Germanic *akaną(“to be bad, be evil”)) and æċe(noun) (from Proto-Germanic *akiz), both from Proto-Indo-European *h₂eg-(“sin, crime”). Cognate with Low German aken, achen, äken(“to hurt, to ache”), North Frisian akelig, æklig(“terrible, miserable, sharp, intense”), West Frisian aaklik(“nasty, horrible, dismal, dreary”), Dutch akelig(“nasty, horrible”).
The verb was originally strong, conjugating for tense like take (e.g. I ake, I oke, I have aken), but gradually became weak during Middle English; the noun was originally pronounced as /eɪt͡ʃ/ as spelled (compare breach, from break). Historically the verb was spelled ake, and the noun ache (even after the form /eɪk/ started to become common for the noun; compare again break which is now also a noun). The verb came to be spelled like the noun when lexicographer Samuel Johnson mistakenly assumed that it derived from Ancient Greek ἄχος(ákhos, “pain”) due to the similarity in form and meaning of the two words.
From Middle English ache, from Old French ache, from Latin apium(“celery”). Reinforced by modern French ache.
Representing the pronunciation of the letter H.
etymonline
ache (v.)
Old English acan "suffer continued pain," from Proto-Germanic *akanan, perhaps from a PIE root *ag-es- "fault, guilt," represented also in Sanskrit and Greek, which is perhaps imitative of groaning.
Originally the verb was pronounced "ake," the noun "ache" (as in speak/speech). The noun changed pronunciation to conform to the verb, but the spelling of both was changed to ache c. 1700 on a false assumption of a Greek origin (specifically Greek akhos "pain, distress," which rather is a distant relation of awe (n.)). Related: Ached; aching.
ache (n.)
"continuing pain," early 15c., æche, ece "an ache, pain," from Old English æce, from Proto-Germanic *akiz, from same source as ache (v.), which see for the unusual evolution of spelling and pronunciation.
