The most common and most likely answer to this crossword clue is the 4 plus 5 letter word SHOT GLASS
S
H
O
T
G
L
A
S
S
More clues leading to the result SHOT GLASS
Buddy explains!
The straight part
We know that "put a drop of gin in it" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case put a drop of gin in it = shot glass.The cryptic/wordplay part
In cryptic crossword there's often an wordplay/cryptic part as well.This part involves a more complex hint, such as an anagram, homophone, hidden word, etc.
Sadly, We don't have an explanation for this specific crossword clue yet.