train vs build up

train is a noun but build up is not a noun.

Word	Noun	Adjective	Verb	Adverb
train	Yes	No	Yes	No
build up	No	No	Yes	No

train (noun)	build up (noun)
public transport provided by a line of railway cars coupled together and drawn by a locomotive
wheelwork consisting of a connected set of rotating gears by which force is transmitted or motion or torque is changed
piece of cloth forming the long back section of a gown that is drawn along the floor
a series of consequences wrought by an event
a procession (of wagons or mules or camels) traveling together in single file
a sequentially ordered set of things or events or ideas in which each successive member is related to the preceding

train (verb)	build up (verb)
exercise in order to prepare for an event or competition	form or accumulate steadily
undergo training or instruction in preparation for a particular role, function, or profession	enlarge, develop, or increase by degrees or in stages
create by training and teaching	change the use of and make available or usable
teach and supervise (someone); act as a trainer or coach (to), as in sports	bolster or strengthen
point or cause to go (blows, weapons, or objects such as photographic equipment) towards	prepare oneself for a military confrontation
drag loosely along a surface; allow to sweep the ground
travel by rail or train
educate for a future role or function
teach or refine to be discriminative in taste or judgment
develop (a child's or animal's) behavior by instruction and practice; especially to teach self-control
cause to grow in a certain way by tying and pruning it