The term 'monokini LACK' is a combination of two words: 'monokini' and 'LACK'. A monokini is a type of swimsuit that covers the torso but leaves the midriff exposed. The word 'LACK' means to be without something or to be deficient in something. Therefore, the term 'monokini LACK' refers to a LACK of coverage for the midriff area when wearing a monokini. The crossword solution for this term is 'BRA', which is an undergarment that provides support and coverage for the breasts.