analog science definition

or analogue

1. An organ or structure that is similar in function to one in another kind of organism but is of dissimilar evolutionary origin. The wings of birds and the wings of insects are analogs.
2. A chemical compound that has a similar structure and similar chemical properties to those of another compound, but differs from it by a single element or group. The antibiotic amoxicillin, for example, is an analog of penicillin, differing from the latter by the addition of an amino group. Compare homologue.