WordNet records no synonym and no antonym for trek. 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 journey by ox wagon (especially an organized migration by a group of settlers)
Synonyms, antonyms and the broader and narrower relations for trek come from Princeton University’s WordNet. Full sources and licences.
journey on foot, especially in the mountains
“We spent the summer trekking in the foothills of the Himalayas”
make a long and difficult journey
“They trekked towards the North Pole with sleds and skis”