user13705: I'm looking for a word that represents the piece after the promotion. In a chemical reaction there are the reactants and the products. Is there an equivalent word for product in promotion?
(In case I haven't make it clear: after a8=Q, is there a word for that queen?)
Edit: I was looking for a generic term (preferably one word) for the resulting piece, not a specific type like queen or knight.
Summarizing some suggestions
The following suggestions are from comments and answers (thank you all) at the time I'm editing this: "promoted piece", "promotee", and "new piece".

user13692: Since I don't reckon any terms describing such things, why don't we create them? 

New born Queen = Princess
  A young Horse/Knight = Foal
  A junior Bishop = Suffragan
  A smaller Rook = Crow  

I know I will face a lot of disagreement, and I'm not sure if people will ever use these stupid terms. 

user8844: It is not clear what you are after, if you are looking for a generic term describing a piece that was added in the game during the play then you seem to be after something that is not embedded in the game. There is no such word and there cannot be any because if there was such a word it would suggest that the new piece is somehow different from an equivalent piece that was there at the beginning of the game. But that is not the case the piece into which the pawn is promoted is absolutely equivalent to another piece of the same name and colour. 
Occasionally it may be useful to refer to a piece that has just been added (but this you seem not to want to do). There are several reasonable suggestions in the comments I will just add that the Laws of chess use "the new piece" for this purpose (as in "... and the effect of the new piece is immediate" or "...when the player's hand has released the new piece on the square of promotion...", articles 3.7.5.3 and 4.7.3, respectively). 

13705: <p>I'm looking for a word that represents the piece after the promotion. In a chemical reaction there are the reactants and the products. Is there an equivalent word for product in promotion?<br>
(In case I haven't make it clear: after a8=Q, is there a word for that queen?)</p>

<p><strong>Edit</strong>: I was looking for a generic term (preferably one word) for the resulting <em>piece</em>, not a specific type like queen or knight.</p>

<p><strong>Summarizing some suggestions</strong><br>
The following suggestions are from comments and answers (thank you all) at the time I'm editing this: "promoted piece", "promotee", and "new piece".</p>
 13692: <p>Since I don't reckon any terms describing such things, why don't we create them? </p>

<blockquote>
  <p>New born Queen = Princess<br>
  A young Horse/Knight = Foal<br>
  A junior Bishop = Suffragan<br>
  A smaller Rook = Crow  </p>
</blockquote>

<p>I know I will face a lot of disagreement, and I'm not sure if people will ever use these stupid terms. </p>
 8844: <p>It is not clear what you are after, if you are looking for a generic term describing a piece that was added in the game during the play then you seem to be after something that is not embedded in the game. There is no such word and there cannot be any because if there was such a word it would suggest that the new piece is somehow different from an equivalent piece that was there at the beginning of the game. But that is not the case the piece into which the pawn is promoted is absolutely equivalent to another piece of the same name and colour. </p>

<p>Occasionally it may be useful to refer to a piece that has just been added (but this you seem not to want to do). There are several reasonable suggestions in the comments I will just add that the Laws of chess use "the new piece" for this purpose (as in "... and the effect of the new piece is immediate" or "...when the player's hand has released the new piece on the square of promotion...", articles 3.7.5.3 and 4.7.3, respectively). </p>
