There are several antonyms for the word "halfassed," which means incomplete, inadequate, or done without proper effort. One of the antonyms is thorough, which is the opposite of shallow or superficial. Another antonym is meticulous, which means careful and precise, in contrast to careless or slapdash. Diligent is also an antonym for "halfassed," pointing to qualities such as hardworking, conscientious, and responsible. On the opposite spectrum, there are terms such as sloppy, haphazard, or slapdash, which are the antonyms of clarity, precision, and purposefulness. When looking for the opposite of "halfassed," one can find numerous words that emphasize excellence, attention to detail, and dedication.