0 I would call it an adverb. It tells 01u00how02u00 to close your eyes. It's a short form of 01i00tightly02i00.02br 00 An adjective would tell 01u00what kind02u00 of eyes. You wouldn't describe someone by saying: 01i00He has tight eyes.02i00 So it's not an adjective.02br 02br