1. (of a personal characteristic) deep-rooted; habitual
1. He has an inveterate distrust of doctors, and has not consulted one in more than thirty years.
2. (of a person) dedicated; tireless; untiring; unwavering
2. The prime minister has a reputation for being an inveterate enemy of corruption.
in (in, into)#vetus veteris (old) (Latin)
In this word. we have a root ie. veter--that have lasted a long time and seem likely to continue. This itself gives an idea of the meaning. World war II veterans. veter is a root which means for a long time