A person who depends on another for support, particularly financial support (= US dependent).
"After my parents retired, they relied entirely on their pension as a dependant during our family's difficult years."
addicted to a drug
"After years of struggling with opioids, he finally checked himself into rehab because he had become completely dependant on heroin."
Obsolete spelling of dependent
"The old legal document lists the applicant's dependant, though modern forms now use the standard spelling."