trainer-n; 4 Senses

Sense Number 1: a person who instructs, coaches others

Commentary: TRAINER[+entity][+person][+instructor]

They took a picture of the championship horse with his jockey and his trainer.
Mary hired a personal trainer at the gym to work with her three days a week.
John is attending a week-long conference to become a trainer for the sales force.

WordNet 3.0 Sense Numbers: 1

Sense Number 2: a simulator, machine that instructs or teaches a skill

Commentary: TRAINER[+entity][+artifact][+machine][+simulator][+instructional]

The airline charges $1500/hour for use of it's flight trainers.
The astronauts practiced hundreds of hours in their trainers before the actual mission.

WordNet 3.0 Sense Numbers: 2

Sense Number 3: person that treats sports teams for minor injuries

Commentary: TRAINER[+entity][+person][+assistant][+medical][+sports_team]

The trainer looked at the player's hand after it was struck by the baseball.
The trainer told the basketball coach that the star player needed to rest his ankle.

WordNet 0.0 Sense Numbers: 3

Sense Number 4: sneaker, athletic shoe

Commentary: TRAINER[+entity][+artifact][+apparel][+shoe][+sneaker]
NOTE: chiefly British usage.

I bought some new trainers for the marathon.
These trainers are good for walking, but not really suitable for running.

WordNet 0.0 Sense Numbers: 4