semi vs tractor trailer

semi and tractor trailer both are nouns.

Word	Noun	Adjective	Verb	Adverb
semi	Yes	No	No	No
tractor trailer	Yes	No	No	No

As nouns, semi and tractor trailer are synonyms defined as:

semi and tractor trailer: a truck consisting of a tractor and trailer together

Other synonyms of semi include articulated lorry, rig, trailer truck, trucking rig.

semi (noun)	tractor trailer (noun)
a trailer having wheels only in the rear; the front is supported by the towing vehicle	a truck consisting of a tractor and trailer together
a truck consisting of a tractor and trailer together
one of the two competitions in the next to the last round of an elimination tournament