Is it ensure, insure, or assure?
mid-14c., from Latin echo, from Greek echo, personified as a mountain nymph, from or related to ekhe "sound," ekhein "to resound," from PIE root *swagh- "to resound" (cf. Sanskrit vagnuh "sound," Latin vagire "to cry," Old English swogan "to resound"). Related: Echoes.
1550s, from echo (n.). Related: Echoed; echoing.