Molten rock (4)
'molten rock' is the definition.
(I've seen this before)
This is all the clue.
(Other definitions for lava that I've seen before include "Emanation from volcano" , "Volcanic discharge" , "Volcanic emanation" , "Molten rock from volcanoes" , "Volcanic outflow" .)
'molten rock' is the definition.
(molten rock from a volcano)
This is the entire clue.
(Other definitions for magma that I've seen before include "Lava" , "hot stuff" , "Semi-fluid material within the earth's crust" , "Glassy volcanic rock" , "Hot fluid rock" .)