Harpsichord ready to take fastener (6)
I believe the answer is:
spinet
'harpsichord' is the definition.
(spinet is a kind of harpsichord)
'ready to take fastener' is the wordplay.
'ready to' becomes 'set' (synonyms).
'take' means one lot of letters goes inside another.
'fastener' becomes 'pin' (pin is a kind of fastener).
'set' going around 'pin' is 'SPINET'.
(Other definitions for spinet that I've seen before include "Small 12" , "organ" , "A small harpsichord of old" , "Old keyboard instrument" , "Early keyboard instrument" .)