Definition of reform. transitive verb. 1a : to put or change into an improved form or conditionb : to amend or improve by change of form or removal of faults or abuses. 2 : to put an end to (an evil) by enforcing or introducing a better method or course of action. 3 : to induce or cause to abandon evil ways reform a drunkard.
The largest horse in recorded history was probably a Shire named Mammoth, who was born in 1848. He stood 21.2 hands (86 inches, 218 cm) high, and his peak weight was estimated at 1,524 kilograms (3,360 lb).
EDIT: As of 2013, the tallest living horse according to the Guinness Book of Records is a Belgian by the name of Big Jake. He is 11 years old and stands 20 hands 2.75 inches (210.2 cm) at the withers.