Loose

Not fixed in place tightly or firmly.
Not held or packaged together.
Not under control.
Not fitting closely
Not compact.
Relaxed.
Not precise or exact; vague; indeterminate.
Indiscreet.
(somewhat dated) Free from moral restraint; immoral, unchaste.
(not comparable, sports) Not being in the possession of any competing team during a game.
(dated) Not costive; having lax bowels.
(of volumes of materials) Measured loosely stacked or disorganized (such as of firewood). Coordinate terms: stacked, solid

Synonyms

(not fixed in place tightly or firmly): unfastened, unsecured
(not held or packaged together): separate, unpackaged
(not bound or tethered or leashed): free, untethered
(not fitting closely): baggy; loose-fitting
(not compact): diffuse, spaced out
(relaxed): loose-limbed, relaxed; carefree
(indiscreet): indiscreet
(promiscuous): polygamous, promiscuous, slutty, tarty, whorish

Antonyms

(not fixed in place tightly or firmly): firm, tight
(not held or packaged together): packaged
(not bound or tethered or leashed): bound, leashed, tethered, tied, tied up
(not fitting closely): close-fitting, snug, tight
(not compact): compact, firm
(relaxed): tense, tensed
(indiscreet): discreet
(promiscuous): faithful, monogamous