Lexical Definition

‎νῆστις‎ nēstis (nace'-tis) fasting ^G:A
from the inseparable negative particle (not) and ‎ἐσθίω‎

fasting.

• not eating, i.e. abstinent from food (religiously)

Abbott-Smith

νῆστις, -ιος, ὁ, ἡ (< νη-, neg. prefix, + ἐσθίω),in cl., chiefly poët., [in LXX: Da LXX 6:18* (19*) (טְוָת)*;]
not eating, fasting: Mt 15:32, Mk 8:3.†

Abbott-Smith References

Liddell-Scott-Jones

νῆστις,

genitive ιος or ιδος, ὁ and ἡ (see. below); also dative νήστει [Refs 5th c.BC+]: (νη-, ἔδω):—not eating, fasting, of persons, ἀνώγοιμι πτολεμίζειν υἷας Ἀχαιῶν νήστιας, ἀκμήνους [νῆστις βορᾶς 5th c.BC: Euripides Tragicus “Iphigenia Taurica” 973: \_metaphorically\_, νῆστιν ἀνὰ.. ψάμμαν">NT+8th c.BC+] over the hungry sand, [Refs 4th c.BC+]

__2 with an abstract substantive, frequently in [Refs 4th c.BC+]famine, [Refs]; νήστισιν αἰκίαις the pains of hunger, Pr.[Refs]; νήστιδες δύαι [Refs]; also νῆστις ὀσμή the bad breath of one fasting, [Refs 5th c.BC+]
__3 active, causing hunger, starving, πνοαὶ νήστιδες [Refs 4th c.BC+]
__II as substantive, νῆστις, ἡ, accusative νῆστιν [Refs 5th c.BC+]
__II.1 the intestinum jejunum, from its always being found empty, [Refs 5th c.BC+]
__II.2 ν. κεστρεύς, fish so called because its stomach was always found empty, [Refs 5th c.BC+]: hence in Comedy texts, of 'empty bellies', ἐγὼ δὲ κεστρεὺς νῆστις οἴκαδ᾽ ἀποτρέχω [Refs 2nd c.AD+]
__II.3 Νῆστις, ἡ, ={ὕδωρ}, [Refs 5th c.BC+]

_{LSJ Scripture Refs: Matt.15.32}