WordNet records no synonym and no antonym for hijab. It is the only member of each of its synsets, which is common for technical, taxonomic and single-sense vocabulary — there is no other English word that means the same thing. The broader and narrower terms below are the useful relations in that case.
Counts are distinct word forms across every sense. A synonym that appears under three senses is counted once here and shown three times below, under each sense it belongs to.
a headscarf worn by Muslim women; conceals the hair and neck and usually has a face veil that covers the face
the custom in some Islamic societies of women dressing modestly outside the home
“she observes the hijab and does not wear tight clothing”
Synonyms, antonyms and the broader and narrower relations for hijab come from Princeton University’s WordNet. Full sources and licences.