Artist and lecturer are a gas (5)
I believe the answer is:
radon
'a gas' is the definition.
(radon is a kind of gas)
'artist and lecturer' is the wordplay.
'artist' becomes 'ra' (Royal Academician, member of Royal Academy of Arts).
'and' says to put letters next to each other.
'lecturer' becomes 'don' (I've seen this before).
'ra'+'don'='RADON'
'are' is the link.
(Other definitions for radon that I've seen before include "Radioactive gas, linked to granite" , "Rare noble gas" , "Naturally occurring inert gas" , "Gaseous element, Rn" , "gets no reaction" .)