One that distends; a thing or person that causes stretching or swelling.
From distend + -er (agent noun suffix). Distend comes from Latin distendere (to stretch apart).
The -er suffix in English is so versatile that we can theoretically make it from any verb—but some agent nouns, like 'distender,' are so rare and abstract that few people ever use them.
Complete word intelligence in one call. Free tier — 50 lookups/day.