Definition of combusts:
(v) :
To burn; to catch fire.
(v) :
(intransitive, figuratively) To erupt with enthusiasm or boisterousness.
(adj) :
(astrology) In close conjunction with the sun (so that its astrological influence is "burnt up"), sometimes specified to be within 8 degrees 30'.
(n) :
(obsolete) That which undergoes burning.
(adj) :
(obsolete) Burnt.