We don't have synonyms for alpha helix yet — it may be a rare, specialized, newly coined, or misspelled word. The closest thesaurus entries we have are alpha-helix.
(n) :
A secondary structure found in many proteins, in which the amino acids are arranged in a coil, or helix, with almost no free space on the inside and all side chains being pointed towards the outside
(n) :
A secondary structure found in many proteins, in which the amino acids are arranged in a coil, or helix, with almost no free space on the inside and all side chains being pointed towards the outside