In the reaction ${\mathrm{CH}}_3\mathrm{CN}+2\mathrm{H} \underset{\mathrm{ether}}{\overset{\mathrm{HCl}}{\to }} \mathrm{X} \underset{{\mathrm{H}}_2\mathrm{O}}{\overset{\mathrm{boiling}}{\to }} \mathrm{Y}$, the term Y is 

In the reaction sequence:

• CH₃CN (acetonitrile) reacts with 2H in the presence of HCl and ether to produce CH₃CH=NH (X).
• The compound X (CH₃CH=NH, ethanimine) reacts with water upon heating (boiling) to produce CH₃CHO (Y) and NH₃.

From the reaction, term Y is acetaldehyde (CH₃CHO).

So, the answer is: Y = acetaldehyde.