Accompaniment and concomitant denote in common something attendant upon or found in association with another thing. Both may imply addition, but they vary chiefly in the kind of relationship connoted between the principal and the attendant things.
Accompaniment often suggests enhancement by the addition of something appropriate.
- the piano accompaniment for a violin solo
- the usual accompaniments of a turkey dinner
- fame is not always the accompaniment of success
Sometimes it stresses concurrence or coincidence rather than causal connection.
- a Roman sedition was the all but invariable accompaniment of a Roman coronation
Concomitant, by contrast, conveys the idea of customary or necessary association.
It does not as a rule need the qualifying words (invariable, essential, inevitable) which so often precede it, for it implies in itself the qualities attributed by these words.
- disruption of routine is the concomitant of illnesses in a staff
- Unemployment is the concomitant of a financial panic
- tuberculosis, hookworm, and infant mortality—the pathological concomitants of pauperism