From out- +‎ burn.

outburn (third-person singular simple present outburns, present participle outburning, simple past and past participle outburned or outburnt)

1. (intransitive) To burn away; be consumed by fire.

   Synonyms: combust, go up; see also Thesaurus:burn

2. (transitive) To exceed in burning; burn longer than.

• burn out, burnout