Regularly jovial and crude? (3)
I believe the answer is:
oil
'crude?' is the definition.
(crude is a kind of oil)
'regularly jovial' is the wordplay.
'regularly' means one should take alternating letters (regularly take one letter, leave next etc.).
The alternating letters of 'jovial' are 'OIL'.
'and' is the link.
(Other definitions for oil that I've seen before include "valuable commodity" , "Lubricating liquid" , "Fluid lubricant" , "Greasy liquid" , "Grease" .)