This term for 2 dissimilar organisms living together in mutualism comes from the Greek for "with" & "life"
The term symbiosis originates from the Greek word Symbioun meaning ... in 
1879 as the living together of two dissimilar organisms, usually in intimate ... a 
mutualisma specific, stable and beneficial association with its host .... the 
advantages that cooperation with microbial partners bring to all life forms.