I just had a look at the Tag list, and found both password and passwords. Obviously we don't need both.
A similar point would be hash and hash-functions.
There also are modes, s-boxes, resources, keys, timing-attacks, side-channel-attacks, elliptic-curves without a corresponding singular form.
All other now existing tags are in singular form.
I suppose in some cases the plural is preferable, in other ones the singular.
Could we find a rule on when tags should be singular and when plural?