eyelash(n = noun.body) cilium, lash - any of the short curved hairs that grow from the edges of the eyelids;
is a kind of hair
is a part of eyelid, lid, palpebra

1.  The fringe of hair that edges the eyelid; -- usually in the pl. [1913 Webster]

2.  A hair of the fringe on the edge of the eyelid. [1913 Webster]

eyelash, n. each of the hairs growing on the edges of the eyelids.

Idiom:
by an eyelash by a very small margin.