Sadhukari or Sadhukaddi is the name of the language used by various Saints (sants) and holy people in northern India before the birth of the first Sikh Guru, Guru Nanak. The word 'Sadhu-kari' has two nodes - 'Sadhu' which means 'holy man' (or holy person) and 'Kari' here means 'artistry' or 'mastery'.
The Sants, Bhagats and Pirs of northern India expressed their beliefs not in the classical Sanskrit language, but in a language which was closely related to that of the common people to whom they addressed their teachings. The basis of this dialect, which has been called Sadhukari was Khari Bolli, mixed with old Rajasthani, Braj (also called Braj Bhasha (ब्रज भाषा), Braj Bhakha (ब्रज भाखा), or Dehaati Zabaan (country tongue), Panjabi and Purvi Boli spoken in what is now eastern Uttar Pradesh.
This language seems to have evolved from various similar "dialects" which, with minor modifications, had been used by the holy Saints all over northern India for many hundreds of years prior to the birth of the founder of Sikhi, Guru Nanak.
The Sadhus (holy men} of India chose the medium for their poetry which could be understood by the common people. Because of this clarity, they were able to influence the masses and bring a change in society. They used words that were in common use in the different dialects that were prominent in this region and this language became known as "Sadhu-kari Bhasha", where Bhasha means 'speak' or language.