Hindi Dictionary (Hindi Sabd Kosh)
Although you'll be better off getting hold of a printed version of English to Hindi and Hindi to English Dictionary, some online versions of Hindi dictionary do exist.
Online Hindi Dictionary
Some Links to Online Hindi dictionaries
Unicode Hindi Dictionary
La Trobe University, Australia has prepared an unicode version of Hindi dictionary. This basic Hindi dictionary contains the vocabulary introduced in the lessons and exercises in their Hindi language study programme. It contains around around 900 words. The explanations of terms given are just working definitions and are not intended to substitute for more complete grammatical explanations, or working through the materials.
Hindi Dictionary Software
Hindi dictionary Software resources are under review and will be featured shortly. Meanwhile you can look in Products section for it.