The term 'ARK UNITS' refers to the measurements used in the Bible to describe the size of Noah's Ark. The three crossword solutions for this term are CUBITS (6 letters), PAIRS (5 letters), and TWOS (4 letters). A cubit is an ancient unit of length, approximately equal to the length of a forearm from the elbow to the tip of the middle finger. PAIRS refer to two of something, such as two animals, and TWOS refer to two of something, such as two of each kind of animal. Together, these three units of measurement were used to describe the size of Noah's Ark in the Bible.