vô căn cứ 
unfounded [ vô ] : (1) in-, im-, (negative prefix); (2) in, at, on; (3) to go into, enter [= vào]
[ căn ] : (1) apartment, flat; (2) [CL for houses, apartments, rooms]; (3) cause, origin, root
[ cứ ] : (1) to continue to, go on, keep on (doing something); (2) evidence, proof; (3) still
Most Common Compounds Set 1:
Most Common Compounds Set 2 :