A noun appearing as G. tunc in the Gnomish Lexicon of the 1910s with various meanings: “chance; occurrence; arrival; hit at shooting; luck” (GL/71). It was related to the verb G. tug- “to hit, reach mark; to light on, chance on, find; to arrive; to chance, occur” and thus was based on the early root ᴱ√TUKU having to do with searching and finding (QL/95).

Neo-Sindarin: The meaning of the root changed to ᴹ√TUK “draw, bring” in Tolkien’s later writings (Ety/TUK). However, I think ᴺS. tunc “chance, occurrence” might be salvaged as a derivation of *tu-n-k-ē “a thing brought” (derived from the root via nasal infixion or metathesis), which at some point gained the sense “a thing brought (unexpectedly)” and hence becoming “chance, occurrence”, divorced from its later verb form [N.] tog- “to bring”.