Necessary bit of tea in a little bottle (5)
I believe the answer is:
vital
'necessary' is the definition.
(thesaurus)
'bit of tea in a little bottle' is the wordplay.
'bit of' indicates taking the first letters.
'in' indicates putting letters inside.
'a little bottle' becomes 'vial' (vial is a kind of bottle. I am not sure about the 'little' bit.).
The first letter of 'tea' is 't'.
't' placed into '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" .)