A lot vs. Alot: 9 Grammatical Pitfalls
also check-up, "careful examination," 1921, American English, from check (v.) + up (adv.), on notion of a checklist of things to be examined. The verbal phrase check up (on) is attested from 1889.
checkup check·up (chěk'ŭp')n.
An examination or inspection.
A general physical examination.