A problem that is very difficult to solve.

Something unpleasant becoming less intense

A shortened form of a word or phrase. For example, AI - Air India.

formally put an end to a system, practice, or institution

the act of abolishing a system or practise or institution

declare someone free from guilt, obligation, or punishment

Become a part of another  

Get added or included in something or with someone  

Fulfil  

Agreement