the main or most important aspect

an organism that lives on or in a host and gets its food at the expense of its host

fundamental or essential

आधारभूत

English Usage: The primary purpose of the meeting is to discuss the new policy.

Hindi Usage: बैठक का आधारभूत उद्देश्य नई नीति पर चर्चा करना है।

a person who habitually relies on or exploits others

निःशङ्क

English Usage: He always mooches off his friends; he's a real parasite.

Hindi Usage: वह हमेशा अपने दोस्तों पर निर्भर रहता है; वह वास्तव में एक निःशङ्क है।