Grand old lady in charge when holding crack (8)
I believe the answer is:
majestic
'grand' is the definition.
(I've seen this in another clue)
'old lady in charge when holding crack' is the wordplay.
'old lady' becomes 'ma' (both can informally mean mother).
'in charge' becomes 'ic' (abbreviation for 'in charge').
'when holding' is an insertion indicator.
'crack' becomes 'jest' (I can't justify this - if you can you should give a lot more credence to this answer).
'ma'+'ic'='maic'
'maic' placed around 'jest' is 'MAJESTIC'.
Can you help me to learn more?
(Other definitions for majestic that I've seen before include "Of noble bearing, like a king" , "Stately; sublime" , "Regal - grand" , "Regal, imperial" , "Impressively beautiful" .)