placebo, n. — Green’s Dictionary of Slang

placebo n.

[Lat. placebo, I shall please; popularized as the name commonly given to Vespers in the Office for the Dead, from the first word of the first antiphon (Placebo Domino in regione vivorum, Ps. cxiv. 9)]

a toady or sycophant; sycophancy.

c.1386		Chaucer Merchant’s Tale line 234: Placebo seyde, o Ianuarie, brother, Ful litel nede had ye, my lord so dere, Conseil to axe of any that is here.
1426		Lydgate (trans.) De Guillaume de Guileville line 22417: Fflateryng [...] Somme callen hir Placebo, ffor sche kan maken an Eccho Answere euere ageyn the same [OED].
1554		J. Knox Godly Letter Aviijb: Nowe they haue bene at the skoole of Placebo, and ther they haue lerned [...] to daunse as the deuill lyst to pype [OED].
1567		J. Knox Hist. of Reformation in Laing Works (1846) I 37: The Bischop [...] having his placeboes and jackmen in the toun, buffatted the Freir, and called him Heretick .
a.1651		D. Calderwood Hist. of the Kirk (1843) II 220: Placeboes and flatterers went to court, t, and told that Mr Knox had spokin against the queen's mariage.

In phrases

hunt a placebo (v.)

to be a toady or sycophant.

c.1367–86

Langland Piers Plowman’s Vision (B) III (1550) line 309: Prestes and persones with placebo to hunt.

make (a) placebo (v.)

to be a toady or sycophant.

1483

W. Caxton (trans.) Knight of the Tower lxxxxiij line 38: He ought not to counceylle hym [...] and not flatere hym ne make the placebo.

play placebo (v.)

to be a toady or sycophant.

1481		W. Caxton Reynard the Fox (1880) xxvii 65: Ther ben many that play placebo [F&H].
1560		Becon Early Works Parker Soc. (1843) 276: He cannot play placebo.
1583		Legend Bishop St Androis Prol. 78: Plaing placebo into princes faces, / With leyis and letteris doing thair devoir.

sing a placebo (v.)

to toady to, to curry favour.

1340		Ayenbite of Inwyt 60: Þe uerþe zenne is þet huanne hi alle zingeþ ‘Placebo’, þet is to zigge: ‘mi lhord zayþ zoþ, mi lhord deþ wel’ [OED].
c.1386		Chaucer Somnour’s Tale line 2075: Singeth Placebo, and I shal, if I can, But if it be un-to a povre man.
1523		Skelton Colyn Cloute (1550) Ciiii: They occupy them so With singing placebo.
1591		J. Harington Ariosto Preface: A smooth-tong’d preacher, that did much affect / To be reputed of the purer sect. / Of which comedie — when some to sing placebo, advised that it should be forbidden, because it was somewhat too plaine .
1594		Gesta Grayorum (1688) 17: A Choir of Nuns, with burning Lamps to chaunt Placebo to the Gentlemen of the Prince’s Privy-Chamber.
1625		Bacon Essays of Counsels xx 74: Counsellors will but take the Wind of him, and instead of giuing Free Counsell, sing him a Song of placebo.
1679		J.P. Letter to a Friend in the Country 3: Where every one would sing a Placebo to the rising Sun [the next Heir to the Crown] [OED].