Mountain ash (5)
'mountain ash' is the definition.
(rowan is a kind of mountain ash)
This is the entire clue.
(Other definitions for rowan that I've seen before include "Man" , "Tree - archbishop" , "Mountain-ash" , "Mountain ash (at Lambeth!)" , "Atkinson or Williams" .)
This clue might be a double definition.
'mountain' is the first definition.
Although both the answer and definition are singular nouns, I cannot see how one could define the other.
'ash?' is the second definition.
(thesaurus)
Can you help me to learn more?
(Other definitions for lava that I've seen before include "Volcanic stuff" , "What volcano ejects" , "Volcanic emanation" , "dangerous fluid" , "Discharge from volcano" .)