Bottle-opener dropped into miniature beer mug? (4)
I believe the answer is:
toby
'beer mug?' is the definition.
(I've seen this in another clue)
'bottle-opener dropped into miniature' is the wordplay.
'opener' suggests taking the first letters.
'dropped into' is an insertion indicator.
'miniature' becomes 'toy' (synonyms).
The first letter of 'bottle' is 'b'.
'b' put into 'toy' is 'TOBY'.
(Other definitions for toby that I've seen before include "dog with frill round neck" , "Mr Punch's dog, beer-jug" , "fellow" , "Member of the 12 [SHANDY] family" , "So-called knight" .)