νυ_νί_ (νῦν + deictic ι_, 333 g) is stronger than νῦν: even now, at this moment; rarely in a causal sense.2926
νυν (enclitic; lyric, tragic, Herodotus, rare and suspected in Homer), a weakened form of νῦν, is rarely temporal, usually inferential, as
κάθιζε νύν με
νύ_ν (enclitic) is adopted by some scholars in Attic tragedy where a long syllable is required (
νυ (enclitic; Epic and Cyprian), a still weaker form of νῦν, and less emphatic than δή. It is common in questions and appeals; less frequent in statements; as τίς νυ; who now? Also after other particles, as καί νύ κε, ἦ ῥά νυ.
Herbert Weir Smyth [n.d.], A Greek Grammar for Colleges; Machine readable text [info] [word count] [Smyth].