In this case, the in-game command is help consider. Typing in consider in search help topics on this site works too. CF has a very good helpfile system, so you'll be likely to get some useful information.

This is what the helpfile would have told you(basically the same info than the other guy posted, but a bit more thorough. The helpfile also points you to the helpfiles of two other attributes, size and alignment, consider gives you beyond the mob level):

CONSIDER VETERAN

Syntax: consider <character>

CONSIDER tells you what your chances are of killing a character. You will
not be able to consider another player unless they are in your pk range.
Of course, it's only a very rough estimate, comparing your level to the
other character/creature's level. Special abilities, immunities, and/or
vulnerabilities are not taken into account. The relative size of your
opponent is given and their alignment. Smiling or greeting creatures are
good, disinterested are neutral, and evil grinners are evil.

The comparison messages, in order from an easy fight to a very hard one:
You could kill a tough Kobold with your little finger.
A rabbit doesn't have a fighting chance.
A rabbit looks like an easy kill.
The perfect match!
A few lucky blows would kill him.
A rabbit shows you his razor-sharp teeth.
A hooded figure waits patiently nearby.

An opponent who has won battles may look more veteran to you when you
use this command. They will be slightly tougher than you otherwise
would suspect.

See also: SIZE, ALIGNMENT

I'd also like to point out that reading the helpfiles for even the simplest skills and commands will probably give some useful information. For example, try reading a helpfile for say if you already haven't to see if it provides any useful information. The see also helpfiles might also be interesting.

You are welcome to ask your questions here or in Dio's but the helpfiles are the fastest way to get answers.