What you should now about Greek adverbs

The Greek adverbs derive from the adjectives.

adjective stem + -α or -ως ending

Adjective	Adverb
ακριβός	ακριβά (expensive), ακριβώς (exactly)
καλός	καλά / καλώς (good)
ψηλός	ψηλά (high)
γρήγορος	γρήγορα (fast)

The comparative is formed by the ending -ότερα or by the word πιο located before the adverb.

Adjective	Adverb
ακριβός	πιο ακριβά / ακριβότερα (more expensive)
ψηλός	πιο ψηλά / ψηλότερα (higher)
γρήγορος	πιο γρήγορα / γρηγορότερα (faster)

Exceptions:
καλός – πιο καλά / καλύτερα (better)
πολύς – πιο πολύ / περισσότερα (more)

Besides there are numerous adverbs with adverbial phrases which are not directly derived by/from an adjective.

The local adverb points to a location, such as εδώ (here), πουθενά (nowhere, παντού (everywhere), εκεί (there), μέσα (inside), έξω (outside), μπροστά (upfront), πίσω (behind)
The causal adverb points to a cause, such as επειδή, γιατί (because/since), μολονότι (although/despite), παρόλα αυτά (nevertheless), γι’αυτό (therefore), γιατί (namely)
The temporal adverb points to notions of time, such as χθες (yesterday), σήμερα (today), τώρα (now), αύριο (tomorrow), φέτος (this year), πέρυσι (last year)
The modal adverb points to the way of doing something, such as πραγματικά (really), φυσικά/βέβαια/βεβαίως (naturally), σκόπιμα/επίτηδες (intentionally/purposely), έτσι (this way), καθόλου (not at all)

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Greek Grammar