symbiont
Concise Oxford English Dictionary © 2008 Oxford University Press:
symbiont /ˈsɪmbɪɒnt, -bʌɪ-/
▶noun Biology an organism living in symbiosis with another.
– origin C19: formed irregularly from Gk sumbiōn ‘living together’, pres. part. of sumbioun (see symbiosis).
'symbiont' also found in these Oxford entries:

