1.
If a business or project goes under , it becomes unable to continue in operation or in existence. ( BUSINESS )
If one firm goes under it could provoke a cascade of bankruptcies.
= collapse
PHRASAL VERB : V P
2.
If a boat, ship, or person in a sea or river goes under , they sink below the surface of the water.
The ship went under, taking with her all her crew.
= sink
PHRASAL VERB : V P