Planetesimal vs. Protoplanet

(astronomy) Any of many small, solid astronomical objects that orbit a star and form protoplanets through mutual gravitational attraction.

(astronomy) Being or relating to one of these astronomical objects.

Example: ‘a planetesimal body’;

one of many small solid celestial bodies thought to have existed at an early stage in the development of the solar system

Planetesimals are solid objects thought to exist in protoplanetary disks and debris disks. Per the Chamberlin–Moulton planetesimal hypothesis, they are believed to form out of cosmic dust grains.

An astronomical object, approximately the size of the Moon, formed from the mutual gravitational attraction of planetesimals; they are thought to collide with each other and slowly form planets

A protoplanet is a large planetary embryo that originated within a protoplanetary disc and has undergone internal melting to produce a differentiated interior. Protoplanets are thought to form out of kilometer-sized planetesimals that gravitationally perturb each other's orbits and collide, gradually coalescing into the dominant planets.