Middle Primitive Elvish
now
root. think, form idea, imagine
si
root. this, here, now
There are more words but they are from Tolkien's earlier conceptional periods. Tolkien likely changed these words as he evolved the aesthetics and completeness of the languages. You may even find languages that Tolkien later rejected. Do not mix words from different time periods unless you are familiar with the phonetic developments.
Below: Tolkien's Late Period (1950–1973). These are from Tolkien's late conceptual period — his most settled forms of the languages. Prefer these over the earlier ones above when composing new text.
A root in The Etymologies of the 1930s given as ᴹ√NOWO “think, form idea, imagine”, with derivatives like ᴹQ. nó “conception” and N. nauth “thought” (Ety/NOWO). It replaced deleted roots ᴹ√ÑŌ¹ and ᴹ√NAWA (EtyAC/ÑŌ¹, NOWO). The latter is a strong indication that its original precursor was the root ᴱ√NAVA [NAɃA] “suspect, guess, have an inkling of” from the Qenya Lexicon of the 1910s with derivatives like ᴱQ. nauma “hint, clue” and ᴱQ. nauta- “guess” (QL/64-65), as well as G. naf- “suspect, have inkling of” and G. naus “keen-witted, observant” from the contemporaneous Gnomish Lexicon (GL/59).