OED: Adjective. Going together, accompanying, concurrent, attendant.
Noun. 1. An attendant state, quality, circumstance, or thing; an accompaniment.
2. A person that accompanies; a companion.
(OED, 2nd Ed, accessed through U of MN Libraries)
Taubes: “Once Hirsch’s obese subjects took to restricting their calories, however, they experienced what he called ‘all the physiological and psychological concomitants of starvation’” (256).
Sentence: Confusion was concomitant with filing the complicated tax return.