Noun

(wikipedia expertise) (-)

Great skill or knowledge in a particular field or hobby

The scientist has expertise in the field of nuclear fusion.

* 2014 , Michael White, " Roll up, roll up! The Amazing Salmond will show a Scotland you won't believe", The Guardian , 8 September 2014:

He spoke of Scotland's hydroelectric projects in Africa, local expertise shared with the world's poor.

advice, or opinion, of an expert

Noun

(uncountable) Mental, sometimes emotional process of comprehension, assimilation of knowledge, which is subjective by its nature.

(countable) Reason or intelligence, ability to grasp the full meaning of knowledge, ability to infer.

(countable) Opinion, judgement or outlook.

* {{quote-magazine, date=2013-08-03, volume=408, issue=8847, magazine=(The Economist)

, title= The machine of a new soul , passage=The yawning gap in neuroscientists’ understanding of their topic is in the intermediate scale of the brain’s anatomy. Science has a passable knowledge of how individual nerve cells, known as neurons, work. It also knows which visible lobes and ganglia of the brain do what. But how the neurons are organised in these lobes and ganglia remains obscure.}}

(countable) An informal contract, mutual agreement.

(countable) A reconciliation of differences.

(uncountable) Sympathy.

All that people individually sense and feel of themselves.