We don't have synonyms for halfpipe yet — it may be a rare, specialized, newly coined, or misspelled word. The closest thesaurus entries we have are half pipe, half-pipe and half-pike.
(n) :
Alternative form of half-pipe. [(skateboarding, snowboarding, skiing, BMX, rollerskating, kickscootering, etc.) A structure used to perform tricks, approximately semicircular in cross-section, resembling the bottom half of a cylinder lying down.]
(n) :
Alternative form of half-pipe. [(skateboarding, snowboarding, skiing, BMX, rollerskating, kickscootering, etc.) A structure used to perform tricks, approximately semicircular in cross-section, resembling the bottom half of a cylinder lying down.]