Webster's 1828 Dictionary
UNPREMEDITATED
a. 1. Not previously meditated or prepared in the mind.
2. Not previously purposed or intended; not done by design.
New American Oxford Dictionary
unpremeditated
un pre med i tat ed |ˌənpriˈmedəˌtātid, -prē -ˌənpriˈmɛdəˌteɪdɪd | ▶adjective (of an act, remark, or state ) not thought out or planned beforehand: it was a totally unpremeditated attack. DERIVATIVES un pre med i tat ed ly adverb
Oxford Dictionary
unpremeditated
un |pre ¦medi ¦tated |ʌnpriːˈmɛdɪteɪtɪd | ▶adjective (of an act, remark, or state ) not thought out or planned beforehand: it was a totally unpremeditated attack. DERIVATIVES unpremeditatedly adverb
American Oxford Thesaurus
unpremeditated
unpremeditated adjective she later regretted her unpremeditated response: unplanned, spontaneous, unprepared, impromptu, spur-of-the-moment, unrehearsed, ad lib, improvised, extemporaneous; informal off-the-cuff, off the top of one's head. ANTONYMS planned.
Oxford Thesaurus
unpremeditated
unpremeditated adjective her unpremeditated reply: unplanned, spontaneous, unprepared, unarranged, uncontrolled, unintentional, unintended, extempore, extemporary, extemporized, extemporaneous, impromptu, ad lib; spur-of-the-moment, on-the-spot, improvised, improvisatory, unrehearsed, unscripted, unstudied, uncontrived, casual; impulsive, hasty, unthinking, natural, involuntary, automatic; Latin ad libitum; informal off-the-cuff. ANTONYMS premeditated, planned.