The definition of inveterate is something longstanding, ingrained or unlikely to change.(adjective)
A person who has smoked for 50 years is an example of someone who would be described as an inveterate smoker.
See inveterate in Webster's New World College Dictionary
Origin: L inveteratus, pp. of inveterare, to make or become old < in-, in + vetus, old: see veteran
See inveterate in American Heritage Dictionary 4
Origin: Middle English
Origin: , from Latin inveterātus
Origin: , past participle of inveterārī, to grow old, endure
Origin: : in-, causative pref.; see in-2
Origin: + vetus, veter-, old; see wet-2 in Indo-European roots.
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