Lexical Definition

‎νεανίσκος‎ neanískos (neh-an-is'-kos) young man ^G:N-M
from the same as ‎νεανίας‎

young man.

• a youth (under forty)

Abbott-Smith

νεανίσκος, -ου, ὁ (dimin. of νεανίας), [in LXX chiefly for נַעַר, also for בָּחוּר, etc.;]
a young man, youth: Mt 19:20, 22, Mk 14:51 16:5, Lk 7:14, Ac 2:17(LXX) 23:18, 22, I Jo 2:13, 14; of an attendant (cf. Ge 14:24, al.): Ac 5:10.†

Abbott-Smith References

Liddell-Scott-Jones

νεανίσκος-ος,

Ionic dialect νεην-, ὁ, (νεάν) youth, young man, [Refs 5th c.BC+]; ν. τὸ εἶδος (nisi to be read νεανικός) [Refs 5th c.BC+]; but in [Refs 5th c.BC+] and the eldest son of Socrates is called νεανίσκος [Refs 5th c.BC+] in later Gr., Wilcken [NT+3rd c.BC+]

__2 ὁ ἐμὸς ν. my young man, i.e. servant, [NT+3rd c.BC+]

_{LSJ Scripture Refs: Matt.19.20 ☩ Mark.14.51}