Tablet mostly enclosed inside drawer (6)
I believe the answer is:
pencil
'drawer' is the definition.
(I've seen this before)
'tablet mostly enclosed inside' is the wordplay.
'tablet' becomes 'pill' ('pill' can be a synonym of 'tablet').
'mostly' means to remove the last letter.
'enclosed' becomes 'enc' (I've seen this in other clues).
'inside' means one lot of letters goes inside another.
'pill' with its last letter removed is 'pil'.
'pil' going around 'enc' is 'PENCIL'.
(Other definitions for pencil that I've seen before include "Graphite stick" , "__-sharpener" , "A writing stick" , "Drawer with graphite in" , "Writing implement with graphite centre" .)