Those discussed in the Whitney text:

Language elements

Semanticity

Associative relationship between the sign and the referent.

Arbitrariness

The semantic relationship is independent of a physical resemblance between the linguistic element and the referent, in contrast to iconic signals.

Discreteness

Messages are based on a discrete rather than continuous repertoire. Different signals must differ by at least one phonological unit.

Duality of patterning

Sounds and meaning: a large number of semantically functional elements (morphemes) can be created from a small number of nonmeaningful elements (phonemes).

Language Use

Openness (productivity)

New messages can be created freely and easily (grammatical and semantic creativity).

Displacement

We can talk about both the here and now and the there and then.

Other features described by Hockett:

The channel

Vocal-auditory channel

The information transmission channel for all linguistic communications is vocal-auditory, from mouth to ear.

Broadcast transmission and directional reception

All linguistic signals are broadcast (as opposed to "tight-beam") and thus directionally received - the hearer can locate the direction of the source.

Rapid fading

Signals have short lives, a consequence of the vocal-auditory channel.

Interchangeablility

Adult members of a speech community are both transmitters and receivers of linguistic signals.

Complete feedback

The transmitter receives the message that is sent.

Generalization

Specialization

Language is specialized for communicating rather than producing any direct effect of the physical energy involved.

Tradition

Linguistic conventions are passed on from generation to generation by teaching rather than by genes.

Prevarication

Linguistic messages may be logically false or meaningless.

Reflexiveness

Language can be used to "talk" about language.

Learnability

A speaker of a language can learn another language.