channel vs back channel

channel and back channel both are nouns.

Word	Noun	Adjective	Verb	Adverb
channel	Yes	No	Yes	No
back channel	Yes	No	No	No

As nouns, back channel is a hyponym of channel; that is, back channel is a word with a more specific, narrower meaning than channel:

channel: (often plural) a means of communication or access
back channel: an alternative to the regular channels of communication that is used when agreements must be made secretly (especially in diplomacy or government)

Other hyponyms of channel include lens, contact, inter-group communication, liaison, link, line of gab, patter, spiel.

channel (noun)	back channel (noun)
a way of selling a company's product either directly or via distributors	an alternative to the regular channels of communication that is used when agreements must be made secretly (especially in diplomacy or government)
a passage for water (or other fluids) to flow through
a television station and its programs
a bodily passage or tube lined with epithelial cells and conveying a secretion or other substance
a path over which electrical signals can pass
(often plural) a means of communication or access
a deep and relatively narrow body of water (as in a river or a harbor or a strait linking two larger bodies) that allows the best passage for vessels
a long narrow furrow cut either by a natural process (such as erosion) or by a tool (as e.g. a groove in a phonograph record)

channel (verb)	back channel (verb)
send from one person or place to another
direct the flow of
transmit or serve as the medium for transmission