Why can't a reverse fission reaction be automatically classified as a nuclear fusion reaction?
The Wikipedia article on Nuclear Fusion starts off:


  In nuclear physics, nuclear fusion is a reaction in which two or more atomic nuclei come close enough to form one or more different atomic nuclei and subatomic particles (neutrons or protons). The difference in mass between the reactants and products is manifested as the release of large amounts of energy.  ...


$\ce{^4He}$ and $\ce{^{27}Al}$ are certainly different than $\ce{^{30}P}$.

The masses of the products however are more than the masses of the reactants 

$$\newcommand{\d}[2]{#1.&amp;\hspace{-1em}#2}
\begin{array}{lrl}
\text{4-He} &amp; 4.&amp;\hspace{-1em}00260325415 \\ 
\text{27-Al} &amp; 26.&amp;\hspace{-1em}98153863\\ \hline
\text{total} &amp; 30.&amp;\hspace{-1em}98414188\\ 
\end{array}$$

$$\newcommand{\d}[2]{#1.&amp;\hspace{-1em}#2}
\begin{array}{lrl}
\text{30-P} &amp; 29.&amp;\hspace{-1em}9783138 \\ 
\text{n}   &amp; 1.&amp;\hspace{-1em}00866491588 \\ \hline
\text{total} &amp; 30.&amp;\hspace{-1em}9869787 \\ 
\end{array}$$

So it would seem that the definition used would require the products to have less mass than the reactants. This seems like a weird definition to me...