flat

From Latin flāre / flātus 'to blow, breathe air.' The core image is moving air with the breath, which generates inflate (blow air into → swell), deflate (let the air out → shrink, dishearten), and conflate (blow together → fuse, merge). Important: this Latin 'blow' root is unrelated to the everyday English adjective flat 'level,' which comes from a Germanic word (flatr).