service dog

noun3

1. •
   A dog which serves people by helping them with activities of daily living, with search and rescue, or with other (non-draft and nonfarming) tasks.
2. •
   A dog which assists the work of military or law enforcement officers.

   • The German Shepherd probably is the top all-round service dog. He had an enviable record with the K-9 Corps during World War II. — 1959
3. •
   (US, Canada) A dog which assists a person who has a physical disability or a mental disability such as post-traumatic stress disorder.

   • A spinal cord injury will confine him to a wheelchair for life. […] He has a service dog and lives alone in a one-bedroom apartment, although there are relatives nearby. — 2007