Acclimate and Accumulate are easily confused words.
The spell-check application of most word processing software programs would not catch a slip-up of these two words. Spell-check is looking for words that aren’t in its dictionary, and words that resemble words in its dictionary but are possibly spelled wrong. Spell-check isn’t perfect. It doesn’t know and can’t guess what word you wanted or what word you meant, it can only judge the words on the page. If you used words that are all spelled correctly, it gives you a pass anyway.
Autocorrect suggests words that start with the same letters. It suggests what word you may want to save time, but quite often, its suggestions couldn’t be more off base and produces humorous results.
Acclimate is a verb. It means to adapt to one’s surroundings in order to be more physically comfortable. In a figurative sense, it can mean making efforts to fit in to a new environment. This can mean changing one’s wardrobe, or something less visible like changing one’s attitude.
Accumulate is a verb. It means objects gathering together, or piling up, to the point of excess.
The following story uses both words correctly:
Acacia noticed the more she tried to acclimate at the office, the more her coworkers would delegate tasks to her. In the course of one week, so many files had accumulated on her desk, they cascaded onto the floor. It took forever to figure out which papers belonged in which files, and few of her new work friends stopped to help.