Tarot card ladies who meet by thorium gaslight? (4,4)

'tarot card ladies who' is the definition.
I know nothing about this answer so I can't tell whether it can be defined by this definition.

'by thorium gaslight?' is the wordplay.
I cannot quite see how this works, but
'by' could be 'with' (I've seen this before) and 'with' is present in the answer.
The remaining letters 'fool' is a valid word which might be clued in a way I don't see.
This explanation may well be incorrect...

'meet' is the link.

Can you help me to learn more?