As a Noun: 1. The knowledge and experience you have of something because you have seen it or done it before. English = familiarity. 2. The comfort you feel with an extreme climate (or anything 'new') because you have now experienced it for a long time and it doesn't bother or surprise you any more. English = acclimatisation. As a Verb or Adjective: 1. To be familiar with something because you have seen it or done it before. English = (be) used to. 2. To be comfortable with an extreme climate (or anything 'new') because you have experienced it for a long time and it doesn't bother or surprise you any more. English = (be) acclimatised to. 3. To become comfortable with something, especially a new or harsh climate, because you have experienced it for a long time and it doesn't bother you any more. English = acclimatise. As Modifier: 1. Used before or after a verb to mean the action was done regularly in the past or was true in the past. English = used to.