Descending through a thin icing layer

For those who seem to be afraid to declare an emergency, I think it would be
equally safe to declare a "Critical" condition, which would draw nearly the
same amount of attention from ATC, but since you don't necessarily require
priority at this point, you don't need to do that yet.

I disagree. "Critical condition" isn't in the AIM's Pilot/Controller
Glossary, so there's no accepted meaning.

There are two levels of emergency, distress and urgency. The AIM (para.
6-1-2) says:

"An aircraft is in at least an urgency condition the moment the pilot becomes
doubtful about position, fuel endurance, weather, or any other condition that
could adversely affect flight safety."

I think that being stuck above icy clouds, low on fuel, certainly qualifies.
If you use the word emergency, you know that the controller will understand
that your situation is serious. Using your own language like "critical" might
not make it clear.

Your other option is to declare "minimum fuel":

"Indicates that an aircraft's fuel supply has reached a state where, upon
reaching the destination, it can accept little or no delay. This is not an
emergency situation but merely indicates an emergency situation is possible
should any undue delay occur."

I much prefer "emergency" for the case we're discussing.

Barry