I. shack 1 /ʃæk/ BrE AmE noun [countable]
[ Date: 1800-1900 ; Origin: Perhaps from shackly 'likely to fall down' (19-20 centuries) , or from Mexican Spanish jacal 'small building' , from Nahuatl xacalli ]
a small building that has not been built very well:
a tin shack
II. shack 2 BrE AmE verb
shack up phrasal verb informal
to start living with someone who you have sex with but are not married to – used to show disapproval
shack up with
She had shacked up with some guy from Florida.
be shacked up
Is she shacked up with anyone?