Although panegyric is normally a noun, it can be used as an adjective as an alternate spelling of panegyrical, which is all that is happening here. It simply means laudatory. Per the OED:
Of the nature of a panegyric or eulogy; publicly or elaborately expressing praise or commendation; eulogistic, encomiastic, laudatory.
Citations for the shorter form of the adjective include:
- A. 1631 Donne Litanie xxiii. Poems (1654) 344 ― In Panegyrique Allelujaes.
- 1706 Maule Hist. Picts in Misc. Scot. I. 17 ― The panegyrick author after a sort doth show.
- 1737 Pope Hor. Epist. ɪɪ. i. 405 ― I’m not used to panegyrick strains.
- 1774 Mason Elegies i. Poems 46 ― Cautious I strike the panegyric string.
Here is an illustrative citation for the more verbose version of the adjective:
- 1755 J. Shebbeare Lydia (1769) I. 405 ― A dead lord··is always to receive honourable interment and a panegyrical epitaph.
The word started showing up in English in the early 1600s, about a hundred years after it first appeared in French, whence it was borrowed from a Latinized version of the original Greek, πανηγυρικός, meaning fit for a public assembly or festival, from πανήγυρις.
The two noun senses in the OED are:
- A public speech or writing in praise of some person, thing, or achievement; a laudatory discourse, a formal or elaborate encomium or eulogy. Const. on, upon, formerly of.
- Elaborate praise; eulogy; laudation.
Here are several citations for the noun senses:
- 1697 Potter Antiq. Greece ɪᴠ. viii. (1715) 227 ― The Company··were some‐times entertain’d with a Panegyrick upon the dead Person.
- 1762 Goldsm. Cit. W. I. Pref. 5 ― In this season of panegyric, when scarce an author passes unpraised either by his friends or himself.
- 1879 Froude Cæsar xxviii. 491 ― After Cato’s death Cicero published a panegyric upon him.