sinker

sinker /ˈsɪŋkɚ/ noun
plural sinkers
sinker
/ˈsɪŋkɚ/
noun
plural sinkers
Britannica Dictionary definition of SINKER
[count]
1 
: a weight used for holding a fishing line or net underwater
2 
baseball : a fast pitch that drops lower as it reaches home plate
— called also sinker ball

hook, line and sinker

— see 1hook