"Ache" originates from the Old English verb acan ("to suffer pain") and noun æce ("a pain"), rooted in the Proto-Germanic akanan and akiz.  It is believed to stem from a Proto-Indo-European root (*ag-es-) potentially imitative of groaning, with related terms in German and Frisian referring to pain, injury, or festering. The spelling shifted from ake (verb) to ache (noun) due to a mistaken 17th-century association with the Greek akhos.  Historically, the verb was spelled ake, but it adopted the noun's spelling (ache) in the 17th century, largely due to Samuel Johnson's dictionary work.  Ache refers to a continuous, dull pain or, metaphorically, a yearning.  

According to the Oxford English Dictionary (OED), the earliest known use of "ache" (both as a noun and a verb) is in the Old English period, which is prior to 1150.  

Ache, encompassing both physical pain and deep emotional heartache, is a fundamental component of storytelling that anchors characters in reality and drives reader empathy. By incorporating ache, writers can deepen emotional stakes, create realistic character development, and make narratives more memorable and impactful. 

The Importance of Ache in Writing Stories: 
Creates Empathy and Connection: Pain is a universal human experience. When characters suffer, readers relate to that suffering, which builds a strong emotional connection to the story. 
Deepens Emotional Stakes: Ache (emotional pain) highlights what a character stands to lose, making their journey more significant and compelling. 
Enhances Realism: Realistic depictions of physical pain—including recovery time and lasting effects—prevent characters from seeming invulnerable and add a layer of truth that makes the story more believable. 
Drives Character Growth: Physical or emotional suffering often forces characters to change, adapt, or overcome, leading to significant character arcs. 
Adds Dramatic Tension: Ache can be used to raise the stakes, placing hurdles in the way of the protagonist, which increases the dramatic tension of the plot. 
Reveals True Character: Similar to a "pearl within a shell," pain serves as a tool to break down a character’s defenses and reveal their true nature. 

Key Considerations for Writing Ache:  
Link Pain to Emotion: Effective storytelling connects physical pain to emotional, psychological, or internal pain. 
Avoid "Over-doing" It: While pain is important, it should be integrated into the plot, not just used to make a scene dramatic. The intensity of the description should match the severity of the pain. 
Utilize Sensory Details: Describing the physical sensations of pain, rather than just stating a character is in pain, creates a more immersive experience for the reader. 
Use "TOMBS" for Depth: To create a fully realized character, consider the Trait (selfishness, naivety), Origin (what caused the pain), Manifestation (how it's shown), Benefits (what they get from it), and Sacrifices involved in the pain. 

Just the facts:

ACHE Definition & Meaning - Merriam-Webster

ACHE Synonyms: 60 Similar and Opposite Words | Merriam-Webster Thesaurus

ACHING Definition & Meaning - Merriam-Webster