PAIN vs. ACHE

There's  a slight difference between the words PAIN and ACHE. Both are most commonly used as nouns which describe an unpleasant sensation or feeling of discomfort usually associated with illness. But are they actually same?

There are some slight differences between those two words.

• ACHE is a feeling of a rather long term discomfort; not sharp enough to call it PAIN. Since it's persistent you may try to ignore it or get used to it. Also, ACHE usually forms compound nouns with body parts, i.e. a headache, a toothache, a backache

e.g.
Weather changes always give me a headache.

• PAIN is often short-lived, sharp and difficult to ignore. It's also more localised. It does not form compound nouns with body parts but rather goes like this: a pain in the leg, a pain in the neck or a leg pain, a neck pain.

e.g.
After falling off the stairs I felt a massive pain in my ankle.

Now look at the difference:
When you cut your finger you feel pain.
In next few days you may have ache in the wounded finger.

Both words are also verbs. However TO PAIN is most commonly replaced with TO HURT.

e.g.
Whenever I spend few hours in front of a PC, my eyes ache terribly.
Your unjust remark pained me. (Your unjust remark hurt me.)

EAT BREAKFAST VS. HAVE BREAKFAST

Do we EAT BREAKFAST or do we HAVE BREAKFAST? I admit I've never given a second thought to the difference between those to expression and never pondered too much as to which one is correct. As the difficulty was drown to my attention let's have a look.

Both EAT BREAKFAST and HAVE BREAKFAST are correct and are practically interchangeable which basically means that you may use them in the same way and they will mean the same thing. 

I usually eat breakfast on my balcony. * I usually have breakfast on my balcony.

To go a step further, verbs EAT or DRINK and HAVE refer to the act of eating or drinking something.

We had a chocolate cake at the party last night. *We ate a chocolate cake at the party last night.

People with high blood pressure shouldn't drink any coffee. * People with high blood pressure shouldn't have any coffee. 

If you like to be more precise, it's worth noting that if your breakfast consists of a glass of orange juice or a mare cup of coffee and a cigarette, then you'd  opt for HAVE BREAKFAST since you're actually not eating anything.

I was in hurry so  I just drank a cup of coffee for breakfast. * I was in hurry so I just had a cup of coffee for breakfast. 

NOTE: Of course same rules apply to lunch and dinner or other meals.