Big  —adj. (bigger, biggest) 1 a of considerable size, amount, intensity, etc. B of a large or the largest size (big toe). 2 important (my big day). 3 adult, elder (big sister). 4 colloq. A boastful (big words). B often iron. Generous (big of him). C ambitious (big ideas). 5 (usu. Foll. By with) advanced in pregnancy (big with child). —adv. Colloq. Impressively or grandly (think big).  in a big way colloq. With great enthusiasm, display, etc.  biggish adj. [origin unknown]