Webster's English Dictionary

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underlie

un.der.lie \-'li-\ vt 1: to be subject or amenable to {~ a challenge}  2: 
   to lie or be situated under  3: to be at the basis of : form the foundation 
   of : SUPPORT {i deas underlying the revolution} 4: to exist as a claim or 
   security superior and prior to (another) {a fi rst mortgage ~s a second}