【Harden】 ,  【season】 ,  【acclimatize】 ,  【acclimate】  denote to make (as a person) proof against hardship, strain, or exposure. All imply a becoming accustomed or adapted by time or experience.

【Harden】 implies habituation that toughens one and makes one insensible of one’s own pain or discomfort or callous and insensitive to others’ misery.

【Season】 implies a gradual bringing into mature, sound, efficient condition; it does not, when referred to persons, necessarily imply that what is to be undergone is uncongenial.

【Acclimatize】  and  【acclimate】 imply adaptation to a new and adverse climate or, by extension, to new and strange surroundings in general.

Some writers have distinguished  【acclimatize】  from  【acclimate】 by restricting the first to adaptation by human agency, but this distinction is not commonly observed.