pain

1 pain /ˈpeɪn/ noun
plural pains
1 pain
/ˈpeɪn/
noun
plural pains
Britannica Dictionary definition of PAIN
1 
: the physical feeling caused by disease, injury, or something that hurts the body
[noncount]
[count]
— see also aches and pains at 2ache
2 
: mental or emotional suffering : sadness caused by some emotional or mental problem
[noncount]
[count]
— see also growing pains
3 
[singular] informal : someone or something that causes trouble or makes you feel annoyed or angry
— often used in phrases like pain in the neck or (impolite) pain in the ass

be at pains

: to try hard to do something

feel no pain

— see 1feel

go to great pains

or take (great) pains
: to be careful in doing something : to try hard to do something — followed by to + verb

no gain without pain

— see 2gain

no pain, no gain

— see 2gain

on/under pain of

formal
: at the risk of being given (a particular form of punishment)
2 pain /ˈpeɪn/ verb
pains; pained; paining
2 pain
/ˈpeɪn/
verb
pains; pained; paining
Britannica Dictionary definition of PAIN
[+ object] formal
: to cause (someone) to feel emotional pain : to make (someone) upset, sad, worried, etc.