Green’s Dictionary of Slang

1. (also hippo) a feeling of mild depression, of being out of sorts.

1709		‘Phoebe Crackenthorpe’ Female Tatler (1992) (4) 8: Several ladies whose constitutions are impaired by the spleen, the hyppo, the flatus and the hurry of the spirits.
1711		B. Mandeville [title] Treatise of the Hypochondriack and Hysterick Passion vulgarly call’d the Hypo in Men and Vapours in Women.
1732		Harlot’s Progress 40: But to be pleasant — Cutting Capers / Cur’d Moll of Hippo, and the vapours.
1752		Modern Quacks Detected 26: To drive away Melancholy from the Spleen, we have the Hypo-drops.
1769		Kentish Gaz. 30 Aug. 3/4: The So Much famed Hypo-Drops. For Hyopocondriack Melancholy in Men, and the Hysteric Diseases or Vapour in Women.
1778		Newcastle Courant 14 Mar. 2/1: The Hypo-Drops [...] a most efficacious medicine in all melancholy and hypochrondriacal afflictions in both sexes.
1818		M.L. Weems Drunkard’s Looking Glass (1929) 128: Poor Tom has fallen into the hypo.
1836		in AS XVI:3 (1941) 235/1: I am homesick... I have had the hyppo, and all sorts of Blues.
1836		Comic Almanack Aug. 61: So, Mister Snip, don’t have the hyp, / Nor look so overcast.
1851		Melville Moby Dick (1907) 169: But thou sayest, methinks this white-lead chapter about whiteness is but a white flag hung out from a craven soul; thou surrenderest to a hypo, Ishmael.
1851		‘The Way Old Bill Went Off’ in T.A. Burke Polly Peablossom’s Wedding 163: He would give up to the ‘hyppo,’ and when in one of his ways, he’d keep his bed for weeks at a time.
1869		H.B. Stowe Oldtown Folks 333: Polly had strictly forbidden us ever to mention that corner of the garret [...] alleging, as a reason, that ‘’t would bring on one her hypos.’ We did n’t know what ‘hypos’ were, but we supposed of course they must be something dreadful.
1895		Journal of Amer. Folklore 8 84: To be low spirited was to have the ‘hypos’.
1966–70		in DARE.

2. (also hippo, hypps) a hypochondriac.

1738		Swift Polite Conversation xx: Some Abbreviations exquisitely refined: As, Pozz for Positively, [...] Hipps, or Hippo for Hypochondriacks.
1788, 1796		Grose Classical Dict. of the Vulgar Tongue (2nd, 3rd edn) n.p.: Hyp. The hypochondriac.
1811		Lex. Balatronicum [as cit. 1788].
1823		Egan Grose’s Classical Dict. of the Vulgar Tongue [as cit. 1788].
1914		E. Wittmann ‘Clipped Words’ in DN IV:ii 126: hypo, from hypochondria or hypochondriac. ‘He’s afflicted with hypo.’ ‘He is a hypo.’.
1944		P. Kendall Dict. Service Sl. n.p.: a hypo . . . a hypochondriac.
1950		Goldin et al. DAUL 105/2: Hypo. [...] 2. A hypochondriac.
1971		N. Smith Gumshoe (1998) 13: ‘Some great people were hypos — Darwin . . . er.’ He struggled to think.

3. (US campus) a notably hard worker.

1902

Boston Globe Sun. Mag. 21 Dec. 7–8: A ‘hypo’ is a fellow who devotes almost all his time to study.