A noun translated “spring” and fully declined as an example of a Strong I noun (SD/430).
Primitive elvish
kelu-
verb. to well up, flow (out swiftly), well forth
kelutā-
verb. to cause to spring forth, start (water) flowing, tap
sirya-
verb. to flow, to flow [smoothly]
sīru
noun. stream
A verb in The Etymologies of the 1930s appearing as its Noldorin-style infinitive sirio “flow”, derived from ON. sirya- under the root ᴹ√SIR “flow” (Ety/SIR). In this document, its Quenya equivalent was ᴹQ. sir- “flow” (Ety/SIR), but by 1948 Tolkien had introduced ᴹQ. sirya- “flow” as well (PE22/114).