clairsemer

To scatter thinly or sparsely — almost always encountered as the adjective clairsemé(e) rather than as an active verb, describing hair, a crowd, or vegetation that's sparse and thin.

• Les arbres clairsèment peu à peu la colline. — The trees thin out gradually across the hill.
• Sa chevelure était clairsemée sur le sommet du crâne. — His hair was thin on the top of his head.
• Le public restait clairsemé malgré la publicité. — The audience stayed sparse despite the advertising.

In practice you'll meet clairsemé almost only as a descriptive adjective, not conjugated as a verb in everyday speech — trying to actively conjugate it (il clairsème) will sound stilted outside technical or literary writing.