Professional in Hindi
-uddhyami
-vyavsaayi

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Note added at 2002-12-12 05:42:06 (GMT)
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Above words are used for a person as a professional
If you are looking for word professional as in following sentence
-its a professional matter
then vyaavsaayik is preferred
i.e yah vaavsaayik maamla hai

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Note added at 2002-12-12 06:30:20 (GMT)
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by thorough profession I guess you mean expert/complete/experienced professional sort of person.
In this context I can figure out following meanings of word thorough

-nipuNa-expert/well trained
-parangat-expert in his work
-manjaahuvaa - specifically used for well experienced/vetaran