1. "A system�s-environment interaction or process by which the environment satisfies the changing requirements of the system". (B. BANATHY, 1973, p.85).
2. "A temporary or lasting modification of the organism's structures under the influence of external factors" (S. SALTHE, 1989, p.189-208).
These definitions are so different as to be somewhat contradictory. While B. BANATHY sees an interaction, SALTHE sees merely a process within the system. In the first case it is the system that governs the process, while in the second one, it is the environment. The process is probably reciprocal. Evolving symbiosis and co-evolution could be examples.
In any case, functional modifications are as important as structural ones.
On the other hand, accomodation relates to individuals and does not normally become fixed in the genetic type, as LAMARCK would have had it (had he known the existence of genes): accommodation acts on the basic type, but does not modify it.
Accomodation may however become lasting, i.e. lead to assimilation, i.e. it may turn into the basis of a permanent adaptation at the individual level. Later on, for example through etiological adaptation, this may become a factor of future evolution.