The term 'opposite of loose' can be answered with two words: 'CHASTE' and 'TAUT'. CHASTE is a 6-letter word that means 'abstaining from extramarital, or from all, sexual intercourse'. It is often used to describe someone who is morally pure. TAUT is a 4-letter word that means 'pulled tight; not slack'. It is often used to describe something that is stretched or held firmly in place. Together, these two words provide an accurate description of the opposite of loose.