perturb

Concise Oxford English Dictionary © 2008 Oxford University Press:
perturb/pəˈtɜːb/

▶verb

• 1 make anxious or unsettled.

• 2 alter the normal or regular state or path of (a system, moving object, or process).

– derivatives
perturbable adjective,
perturbative adjective
perturbingly adverb.

– origin ME: from OFr. pertourber, from L. perturbare, from per- ‘completely’ + turbare ‘disturb’.