Echo has the ch said as k, which marks the Greek letter chi, and it came to English in the mid-1300s through Latin from Greek ēkhō. The Greek word is related to ēkhē, "sound," and ēkhein, "to resound," from an ancient root for resounding that also produced Latin vagire, "to cry," and Old English swogan, "to resound."
In classical mythology the sound was personified as a mountain nymph, Echo, who pined away for love of Narcissus until nothing was left of her but her voice — one of the rare cases where the story and the etymology point the same way rather than the story being invented to explain the word. English used the noun for two centuries before making a verb of it in the 1550s.
echo (n.) mid-14c., "sound repeated by reflection," from Latin echo , from Greek ēkhō , personified in classical mythology as a mountain nymph who pined for love of Narcissus until nothing remained but her voice. It is from or related to ēkhē "sound," ēkhein "to resound," from extended form of PIE root *(s)wagh- "to resound" (source also of Sanskrit vagnuh "sound," Latin vagire "to cry," Old English swogan "to resound"). Related: Echoes . Also see echo chamber . also from mid-14c. echo (v.) 1550s (intrans.), c. 1600 (trans.), from echo (n.). Related: Echoed ; echoing . also from 1550s