celon ~ river
nen ~ water
duin ~ (long and large) river
Falathlorn: Falath (from falas) meaning beach or wave-beaten shore and lorn meaning quiet water, anchorage or harbour. Shore of the quiet water.
Celondim: Celon meaning river and im meaning dell or deep vale. Edit: the second root is actually dîm (sadness) to make River of Sadness.
Baranduin: Baran meaning golden-brown and duin meaning river. More famously known as the Brandywine river.
Nenuial: Nen meaning water and uial meaning twilight. Generally known as Lake Evendim.
Nen Harn: Nen meaning water and harn meaning southern. Edit: the root is actually sarn (stone) to give Lake of Stone. (image from lotro wiki)
(Translations are from the Appendix: Elements in Quenya and Sindarin, The Silmarillion, J.R. R. Tolkien or Hiswelókë’s Sindarin Dictionary. I am not an expert at all – if you see any mistakes please let me know! Edits are from this thread here)