In PE:17 page 141 we learn that (some) Sindar called the Exiled Noldor
_eglon_ from the etymon _etlô_.
Just one line over that statement we have the plurial form _Etlôi_,
which gave the S. _igli_; but on top of that same page we read :
Could this _igil_ be a misprint for _igli_?
[I've checked my photocopy of this ms., and the reading "_eglir,
igil_" in the passage cited is certainly correct. In this text Tolkien
was experimenting with a great many possible Sindarin developments
from original _*etlô, *etlôi_, and on pg. 142 you will see that these
include BOTH _igli_ and _igil_, as well as alternative sg. forms such
as _egol_ and _egel_. -- PHW]