Loneliness and solitude
Both denote lack of contact with people!

But

Loneliness is a sense of isolation
Solitude is a sense of seclusion
Loneliness is an emotional response unpleasant
Solitude is an emotional response pleasant

Loneliness can be felt even when surrounded by people
Solitude cannot be felt when surrounded by people
Loneliness is a powerful feeling of emptiness
Solitude is a powerful feeling of fullness

Loneliness includes social factor that is thrust
Solitude includes social factor that is choicest
Loneliness is caused by lack of friendship
Solitude is caused to give others a skip

Loneliness visits every human soul at sometime
Solitude is frequent to human souls sublime
Loneliness is a feeling of being disconnected from others
Solitude is not a feeling of being disconnected from others

Loneliness expresses the pain of being alone
Solitude expresses the glory of being alone
Loneliness has negative effects on individuals
Solitude has positive effects on individuals

Loneliness is a social pain
Solitude is a social gain
Loneliness sends one to a pit of despair
Solitude leads one to the acme to prepare

Loneliness is an attitude—causing anxious feelings
Solitude is an attitude—causing joyous feelings
Loneliness is a subjective experience
Solitude is an objective experience

Loneliness plays the part when in distress
Solitude plays the part in creative process
Loneliness, in short, is when one is unhappy to be alone
Solitude, in short, is when one is happy to be alone!