Force to speak aloud (6)
I believe the answer is:
torque
'force' is the definition.
(torque is a kind of force)
'speak aloud' is the wordplay.
'speak' becomes 'talk' ('talk' can be a synonym of 'speak').
'aloud' shows a homophone (sound like).
'talk' sounds like 'TORQUE'.
'to' is the link.
(Other definitions for torque that I've seen before include "Rotating force" , "Rotational force; necklace" , "Metal necklace; also a measure of force" , "Source of spin" , "Force tending to turn" .)