Necessary bit of tea in a little bottle (5)
I believe the answer is:
vital
'necessary' is the definition.
(I've seen this in another clue)
'bit of tea in a little bottle' is the wordplay.
'bit of' suggests taking the first letters.
'in' means one lot of letters goes inside another.
'a little bottle' becomes 'vial' (vial is a kind of bottle. I am not sure about the 'little' bit.).
The initial letter of 'tea' is 't'.
't' inserted inside 'vial' is 'VITAL'.
Can you help me to learn more?
(Other definitions for vital that I've seen before include "Essential, life-giving" , "Desperately important" , "Spirited" , "Urgently needed or absolutely necessary" , "Essential to life, indispensable" .)