The dispenser is the one who let it slip (7)
I believe the answer is:
'the dispenser' is the definition.
The answer and definition can be both man-made objects as well as being singular nouns.
Maybe there's a link between them I don't understand?
'the one who let it slip' is the wordplay.
I cannot quite understand how this works, but
'one' could be 'o' (I've seen this in other clues) and 'o' is located in the answer.
'who' could be 'dr' (from TV series Doctor Who) and 'dr' is found within the answer.
'it' could be 'e' ('e' can mean 'electronic' which is similar to 'IT') and 'e' is found within the answer.
This explanation may well be incorrect...
'is' is the link.
Can you help me to learn more?
(Other definitions for dropper that I've seen before include "Small tube with a rubber bulb at one end" , "Tube for applying a small amount of liquid" , "One can't catch" , "something in the dispensary" , "Short glass tube with a rubber bulb" .)