rill vs runnel

rill and runnel both are nouns.

Word	Noun	Adjective	Verb	Adverb
rill	Yes	No	No	No
runnel	Yes	No	No	No

As nouns, rill and runnel are synonyms defined as:

Other synonyms of rill include rivulet, run, streamlet.

rill (noun)	runnel (noun)
a small stream	a small stream
a small channel (as one formed by soil erosion)