send vs express-mail

send and express-mail both are verbs.

Word	Noun	Adjective	Verb	Adverb
send	No	No	Yes	No
express-mail	No	No	Yes	No

As verbs, express-mail is a hyponym of send; that is, express-mail is a word with a more specific, narrower meaning than send:

Other hyponyms of send include express, airmail, register.

send (verb)	express-mail (verb)
cause to be directed or transmitted to another place	send by express mail or courier
transfer
broadcast over the airwaves, as in radio or television
assign to a station
to cause or order to be taken, directed, or transmitted to another place
transport commercially
cause to go somewhere
cause to be admitted; of persons to an institution