Here's what the OED has to say about <b>ignis fatuus</b>:
<p>
If we ask the electronic OED for ALL occurrences of 'ignis fatuus, it 
returns this list of entries:
<pre>
> Oxford English Dictionary
> 
> --------------------------------------------------------------------
> Found: 35 entries  (ignis fatuus)
> --------------------------------------------------------------------
> 
>   1. again
>   2. Dick
>   3. elf
>   4. elude
>   5. fatuous
>   6. fatuus
>   7. fen
>   8. feu follet
>   9. fire
>  10. fool
>  11. foolish
>  12. friar
>  13. Friar Rush
>  14. genius
>  15. gillian
>  16. Helena
>  17. Hob
>  18. ignis fatuus
>  19. illume
>  20. indenture
>  21. Jack-o'-lantern; Jack-a-lantern
>  22. kicksey-winsey
>  23. meteor
>  24. Montanist
>  25. night-fire
>  26. phosphuretted
>  27. scatter
>  28. shine
>  29. spritish
>  30. spumy
>  31. take
>  32. tripartite
>  33. trudge
>  34. wild-fire; wildfire
>  35. will-o'-the-wisp
</pre>
Looking at the 'ignis fatuus' entry itself:
<pre>
> OED Entry Search
> 
> --------------------------------------------------------------------
> 
> ignis fatuus
> 
> ignis fatuus i.gnis fæ;tiu,As . med. or mod.L., = foolish fire. A
> phosphorescent light seen hovering or flitting over marshy ground,
> and supposed to be due to the spontaneous combustion of an
> inflammable gas (phosphuretted hydrogen) derived from decaying
> organic matter; popularly called Will-o'-the-wisp, Jack-a-lantern,
> etc. It seems to have been formerly a common phenomenon; but is now
> exceedingly rare.
> 
> When approached, the
> 
> ignis fatuus
> 
> ignis fatuus appeared to recede, and finally to vanish, sometimes
> reappearing in another direction. This led to the notion that it was
> the work of a mischievous sprite, intentionally leading benighted
> travellers astray. Hence the term is commonly used allusively or
> fig. for any delusive guiding principle, hope, aim, etc.
> 
>    * 1563 W. Fulke Meteors (1640) 11 b, This impression seene on the
>      land, is called in Latine, Ignis fatuus, foolish fire, that
>      hurteth not, but only feareth fooles.
> 
>    * 1658 Phillips, Ignis fatuus, a kind of slight exhalation set on
>      fire in the night time, which ofttimes causeth men to wander
>      out of their way.
> 
>    * 1663 Butler Hud. i. i. 509 An Ignis Fatuus that bewitches And
>      leads Men into Pools and Ditches.
> 
>    * 1688 J. Clayton in Phil. Trans. XVII. 789 Ignes fatui, tho
>      there be many boggy Swamps and Marshes, are seldom, if any are
>      seen there.
> 
>    * 1774 Goldsm. Nat. Hist. (1862) I. xxi. 134 Floating bodies of
>      fire..the ignis fatuus, or wandering fire.
> 
>    * 1813 Sir H. Davy Agric. Chem. i. (1814) 26 To avoid being led
>      astray by the ignis fatuus the most secure method is to carry a
>      lamp.
> 
>      fig.
> 
>    * 1599 Broughton's Lett. xii. 40 To fetch light from their
>      Heathenish Ignis fatuus.
> 
>    * 1631 Star Chamb. Cases (Camden) 31 For Sr Arthur Savage, he is
>      the primum mobile, the ignis fatuus that misleades all the
>      rest.
> 
>    * 1777 J. Adams in Fam. Lett. (1876) 264 What an ignis fatuus
>      this ambition is?
> 
>    * 1824 Byron Juan xv. liv, Following the `ignes fatui' of
>      mankind.
> 
>    * 1896 Dk. Argyll Philos. Belief Pref. 7 That ignis fatuus of the
>      time-uniformity of worship throughout the three kingdoms.
> 
>      attrib.
> 
>    * 1808 Byron To youthful friend xvii, An ignis-fatuus gleam of
>      love.
</pre>
And a related term:
<pre>
> OED Entry Search
> 
> --------------------------------------------------------------------
> 
> feu follet
> 
> feu follet fö fole. Fr., lit. `frolicsome fire'. Ignis fatuus.
> 
>    * 1832 J. S. Mill Let. 17 July (1910) I. 32 It is possible our
>      light may be nothing but a feu follet.
> 
>    * 1967 Times 7 Sept. 7/5 He [sc. Flaubert] pursued what one must
>      surely regard as the feu follet of `pure form'.
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