Definition of parasymbiosis in US English:

parasymbiosis

noun

Biology
  • Originally: a relationship in which a lichen supports another lichen or fungal species growing in close association with it, without apparent disadvantage. Later more widely: a commensal or other association short of full mutualistic symbiosis.

Origin

Late 19th century; earliest use found in Journal of the Royal Microscopical Society. From para- + symbiosis, after German Parasymbiose.