Source : Webster's Revised Unabridged Dictionary (1913)

Incautious \In*cau"tious\, a. [Pref. in- not + cautious: cf. L.
   incautus.]
   Not cautious; not circumspect; not attending to the
   circumstances on which safety and interest depend; heedless;
   careless; as, an incautious step; an incautious remark.

Source : WordNet®

incautious
     adj 1: lacking in caution; "an incautious remark"; "incautious
            talk" [ant: {cautious}]
     2: without out proper caution; "an incautious step sent her
        headlong down the stairs"
     3: displaying or feeling no wariness; "an unguarded remark";
        "spilled the beans in an incautious moment" [syn: {unguarded}]