Enter home quietly removing contents of unit (5)
I believe the answer is:
input
'enter' is the definition.
(I've seen this in another clue)
'home quietly removing contents of unit' is the wordplay.
'home' becomes 'in' ('he's home' can mean 'he's in').
'quietly' becomes 'p' (p for piano and quiet).
'removing' becomes 'u' (I can't justify this - if you can you should believe this answer much more).
'contents of' means to look at the middle letters (the letters on the inside of the word).
'unit' becomes 'katal' (SI unit of catalytic activity).
The central letter of 'katal' is 't'.
'in'+'p'+'u'+'t'='INPUT'
Can you help me to learn more?
(Other definitions for input that I've seen before include "Data contributed" , "store" , "Person's contribution (to activity); electrical signal" , "Comment, contribution" , "Contribution; enter (data)" .)