; ο, του, τωι, τον; οι, των, τοις, τους.
; η, της, την, την; αι, των, ταις, τας.
; το, του, τωι, το; τα, των, τοις, τα.

; σ-ος-ι-α; ες-ων-σι(ν)-ας

; ειμί, ει, εστι(ν); εσμεν, εστε, εισι(ν)

I. Common Particles & Enclitics (Small Words)

These often add flavor or logical connections and are sometimes “enclitic,” meaning they attach to the end of the previous word.

γε (ge): "At least," "certainly," "indeed" (emphatic).
τοι (toi): "Let me tell you," "surely" (often strengthens assertions).
τε (te): "And" (enclitic; often links closer than kai).
δὲ (de): "And," "but," "however" (postpositive, often balances a men).
μέν (men): "On the one hand," "indeed" (prepares the reader for a contrast, usually de).
οὖν (oun): "Therefore," "then," "really" (marks a result or continuity).
ἄρα (ara): "Then," "as it seems," "therefore."
γάρ (gar): "For," "because."
περ (per): "Very," "just," "even" (intensifier).
δή (dē): "Indeed," "now" (emphatic). 

II. Indefinite/Interrogative Pronouns & Adverbs (Often Enclitic)

τις, τι (tis, ti): "Anyone," "anything," "someone," "something".
που (pou): "Somewhere," "perhaps," "I suppose".
πως (pōs): "Somehow," "in any way".
ποτε (pote): "Ever," "at some time," "once".
ποι (poi): "To some place," "to any place".
ποθεν (pothen): "From somewhere," "from anywhere". 

III. Common Conjunctions & Subordinators

καὶ (kai): "And," "also," "even."
ἀλλά (alla): "But," "however."
ὡς (hōs): "As," "that," "how."
εἰ (ei): "If."
ἵνα (hina): "In order that."
ἐπεί (epei): "When," "since," "after."

IV. Small Prepositions (Often acting as pre-verbs)

ἐν (en): "In," "on," "among" (+ dative).
ἐκ/ἐξ (ek/ex): "Out of," "from" (+ genitive).
εἰς (eis): "Into," "to," "for" (+ accusative).
σὺν (syn): "With," "together with" (+ dative).
πρὸ (pro): "Before," "in front of" (+ genitive).
πρὸς (pros): "To," "towards," "near" (+ acc/gen/dat). 

V. Modal “Auxiliary” Verbs

These are often used with infinitive forms.

δεί (dei): "It is necessary," "one must".
χρή (chrē): "It is fitting," "one ought".
μέλλω (mellō): "I am about to," "I intend to".
δύναμαι (dynamai): "I am able," "I can".
ἔξεστι (exesti): "It is allowed," "it is possible".