sleeted

'Barb'd with the sleeted snow, the driving hail, / Rush the fierce arrows of the polar gale' (Elegy on Captain Cook, p. 5)

1849, 1884

1780

69

OED1/2 defines s.v. sleet, v., as 'beaten upon, or covered with, sleet'.

insurgent, adv.

''Tis the vex'd billows, that insurgent rave, / Their white foam silvers yonder distant wave' (Elegy on Captain Cook, p. 17)

N/A; corresponding adjectival sense: 1849, 1893 only

1780

69

OED1/2 has no example of adverbial use of this word. Its record of insurgent as an adjective begins with 1814 (Scott) for sense 1, 'Rising in active revolt', and with 1849 (M. Arnold) for sense 2, 'Of the sea or a flood: Surging up or rushing in'. Earlier examples can be found on ECCO.

sun-gilt

'When the sun-gilt day illumes its charms' ('Hoyle Lake', in Llangollen Vale, p. 17)

1807, 1837-42

1794 (1796)

11

See OED1/2 s.v. sun 12b.

silvering

'Like leafless forests...Rise the tall masts...Silvering, and shining in the solar beam' ('Hoyle Lake', in Llangollen Vale, p. 19)

1801, 1818, 1873

1794 (1796)

7

OED1/2 's first quotation is from Southey. Definition: 'That silvers; making or becoming silvery'.

arrowy

'That gives the diamond's eye to blaze / With all thy bright and arrowy rays' [addressed to the sun] ('Ode to the Sun', p. 20)

1785 (Cowper), a1822 (Shelley), 1824, 1861, 1868

1779

6

OED1/2 treats in a catch-all category s.v. 2c: 'in action, effect, etc.; darting, piercing, keen'. As often, Seward is in good poetic company (see discussion of her conventional poetic diction).

steep, v.¹

'When gather'd fogs the pale horizon steep' ('Hoyle Lake', in Llangollen Vale, p. 16)

1798, 1817, 1860, 1887, 1890

1794 (1796)

2

This is OED1/2 sense 1d: 'transf. Of mist, vapour, smoke, light: To "bathe", envelop like a flood'. NB quotations are from favourite sources: '1798 COLERIDGE Anc. Mariner VI. xvii, The moonlight steeped in silentness The steady weathercock. 1817 SHELLEY Rev. Islam I. ii, Long trains of tremulous mist began to..steep The orient sun in shadow...'.