Cross as new missus gulps gallon (6)
I believe the answer is:
bridge
'cross' is the definition.
(I know that bridge is a type of cross)
'new missus gulps gallon' is the wordplay.
'new missus' becomes 'bride' (I can't justify this - if you can you should give a lot more credence to this answer).
'gulps' means one lot of letters goes inside another.
'gallon' becomes 'g' (abbreviation for the unit of liquid).
'bride' going around 'g' is 'BRIDGE'.
'as' acts as a link.
Can you help me to learn more?
(Other definitions for bridge that I've seen before include "Viaduct" , "link" , "Something of a nose" , "going across river?" , "One on the fiddle" .)