n (chiefly countable) A conifer of the genus Abies.
n (chiefly countable) Any pinaceous conifer of related genera, especially a Douglas fir (Pseudotsuga) or a Scots pine (Pinus sylvestris).
n (uncountable) Wood of such trees.
n (aviation) Initialism of flight information region; a specified region of airspace in which a flight information service (FIS) and an alerting service (ALRS) are provided [(aviation) A specified region of airspace in which a flight information service and an alerting service are provided.]
n (South Asia, Singapore, law enforcement) Initialism of first information report.
n (uncountable) Abbreviation of far infrared or far infrared radiation.