1happening or coming immediately:the offence justified instant dismissal prepared quickly and with little effort:we can’t promise instant solutions (of food) processed to allow very quick preparation:instant coffee (of a person) becoming a specified thing immediately:become an instant millionaire
2 dated urgent; pressing: an instant desire to blame others when things go wrong
3 [postpositive] dated (in business letters) of the current month:your letter of the 6th instant
4 archaic of the present moment.
1a precise moment of time:come here this instant! at that instant the sun came out 2a very short time; a moment:for an instant the moon disappeared
3 [mass noun] informal instant coffee.