Here's how I explain 'jinx' to friends who speak Tamil: the basic idea is someone or something that seems to bring bad luck. In English we say 'jinx' for a curse, hex, or even a streak of unfortunate events, and in Tamil the closest single-word fit is usually 'சாபம்' (saapam) — which literally means 'curse' or 'ominous fate'. For a person who always seems to cause mishaps I might call them 'அதிர்ஷ்டக்காரர்' (athirshthakkaarar) — a casual compound that literally means 'luck-maker' but used sarcastically for someone who brings bad luck.
If I want to use a verb-like phrase in Tamil for 'to jinx', I tend to say 'சாபமிட்டுவிட்டாய்' (saapamittuvittai) or more colloquially 'நீ சாபமிட்டாய்' meaning 'you jinxed it' or 'you brought the bad luck'. In everyday speech people also say 'என்னோட அந்த விஷயம் சாபம்தானே' to grumble when a plan goes wrong, which reads like 'that thing of mine is jinxed'.
Culturally, Tamil speakers will switch between formal Sanskrit-influenced words and streetier phrases depending on the vibe — 'தீபவாசி' type words are rare for this concept, so 'சாபம்' plus short phrases are the natural fit. Personally, using those Tamil lines makes the superstitions sound more vivid to me — it feels like the language carries the mood of a small, inevitable mischief.