From Wiktionary, the free dictionary
Literally, “kill flies with cannon-fire”.
matar moscas a cañonazos (first-person singular present mato moscas a cañonazos, first-person singular preterite maté moscas a cañonazos, past participle matado moscas a cañonazos)
- (idiomatic) to use a sledgehammer to crack a nut
