cap ‧ size /kæpˈsaɪz $ ˈkæpsaɪz/ BrE AmE verb [intransitive and transitive]
[ Date: 1700-1800 ; Origin: Perhaps from Spanish capuzar 'to sink a ship front-end first' , from cabo 'head' + chapuzar 'to dive' ]
if a boat capsizes, or if you capsize it, it turns over in the water