Gadee, means seat or throne. Gaddi, and similar sounding phonetically spelled Gurmukhi words, nearly indistinguishable to the Western ear, can mean cushion, pad, seat, throne, or inauguration of a holy being, the seat or driver of a cart, carriage, or wagon, and road way.
In Sikhism, gadee, or gaddi, refers to inauguration of the scripture Guru Granth Sahib, guide to divine enlightenment, and the inaugural ceremonies honoring the Guru's ascension to temporal throne and spiritual seat of supremacy.
Throughout history, Sikhs have revered their gurus as having the exalted status of an emperor, second only to the divine. The first three guru's were unrelated by family ties, and chose as their successor the most humble and serviceable of their Sikh. The fourth through tenth gurus were of Sodhi lineage. Though the succession remained within the Sodhi family, the reigning guru chose as his successor the most humble and serviceable of his descendants. Sixth Guru Har Govind established a physical throne when he raised the Akal takhat, seat of supremacy, at Harmandir Sahib, known today as the Golden Temple. Tenth Guru Gobind Singh bequeathed the succession and throne to the holy scripture Guru Granth Sahib.
The words gadee and gaddi are used in gurpurab date expressions Guru Gadee Day and Guru Gaadi Diwas (day) when referencing commemorative inaugural processions celebrating the anniversary of the October 7, 1708, inauguration of Guru Granth Sahib. On holidays celebrating inaugural festivities, the Guru Granth Sahib is ceremoniously carried out of the gurdwara and placed atop a cushioned cot at a place of prominence on a decorated motorized carriage designated as the float at the head of a procession of devotees parading through the streets.
"Kitarrae lakh jalaebadaar gaaddee-vaan chalaaee gaddeeraa||
There are millions of officers and drivers of royal carriages." Bhai Gurdas || Var 8
"Gurmukh gaaddee raahu sach nibaaheea||
For those who follow gut Enlightener the beautiful highway of Truth has been prepared." Bhai Gurdas || Var 19
"Sach vanaj khaep lai chalae gurmukh gaaddee raahu neesaanee||
Truthful merchandise is loaded fully and carted by followers of the Enlightener's wisdom along the familiar highway." Bhai Gurdas || Var 29