com-plain / kəm-plān
1. to express unhappiness, grief, pain or dissatisfaction
No attention is paid to him who is always complaining.
2. to make a formal accusation of wrongdoing
Any person aggrieved by such disturbance of the peace may complain to the Police about such unreasonable or excessive noise.
Noise Control Ordinance § 16-26.6 Disturbing the Peace., Boston, MA
Through the Old French verb complaindre (complain) from the Late Latin combination of the intensifying prefix -com/-con and the verb plango, plangere, planxi, planctus (strike, beat, beat the breast, grieve, lament).
Thank you to Allen Ward for providing this etymology.