enneiger

To cover with snow — almost always encountered in its past participle enneigé(e), describing snow-covered mountains, roads, or landscapes (les sommets enneigés). The active verb form itself is rarely conjugated outside that adjectival use.

• La neige a enneigé toute la vallée pendant la nuit. — The snow covered the whole valley overnight.
• Les routes enneigées ralentissent la circulation. — The snow-covered roads are slowing down traffic.
• Les pistes sont bien enneigées cette saison. — The slopes are well covered with snow this season.

Learners rarely misuse the meaning, but they do often try to conjugate it actively in contexts where French would simply use the adjective enneigé — 'la route est enneigée,' not some awkward active construction.