guys.. what's different between den, lair and nest. How do I know the difference?

Question

Answer

Birds = Nest.  Usually romantic connotation.  e.g. 'Love nest'

Den = Dragons!  Also often connected with thieves, prostitutes, drug addicts and other fun to be with people.

Lair - any wild animal shelter.  again, negative connotation.

Answer

Den and lair are synonyms as far as im concerned. A nest is where birds live and keep their eggs. 
You may hear such expressions as 
"A nest of criminals" in literature.

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