For old chemist, too bad not to have these days back (4)
I believe the answer is:
boot
'for old chemist' is the definition.
I can't judge whether this defines the answer.
'too bad not to have these days back' is the wordplay.
'not to have' indicates named letters should be taken away.
'these days' becomes 'AD' (as in Anno Domini, after Christ).
'back' says the letters should be written backwards.
'bad' with 'ad' taken away is 'b'.
'too'+'b'='toob'
'toob' back-to-front is 'BOOT'.
Can you help me to learn more?
(Other definitions for boot that I've seen before include "Kick; footwear" , "eg Wellington" , "Hard kick (colloq.)" , "Sturdy shoe; start (a computer)" , "Hard kick; part of car" .)