Etymology 1 
Middle English fely, from Old English felge, dative of felg, from Proto-Germanic *felgōn (cf. East Frisian feelge, Dutch velg, German Felge), from Proto-Indo-European *pl̥g̑ʰ- (cf. Polish płoza 'sliding iron', Old Church Slavonic plĭzati 'to creep, crawl').
felly (plural fellies)
- The outer rim of a wheel, supported by the spokes.
- 1602, Hamlet by William Shakespeare, act 2 scene 2 lines 426-430:
- all you Gods, / In generall Synod take away her power: / Breake all the Spokes and Fallies from her wheele [...].
- 1922, James Joyce, Ulysses:
- The felly harshed against the curbstone: stopped.
Alternative forms 
Etymology 2 
From fell + -ly.
felly (comparative more felly, superlative most felly)
- (now rare) Fiercely, harshly.
- 1590, Edmund Spenser, The Faerie Queene, II.vi:
- Ioues dreaded thunder light / Does scorch not halfe so sore, nor damned ghoste / In flaming Phlegeton does not so felly roste.