Zero  n. (pl. -s) 1 figure 0; nought; nil. 2 point on the scale of a thermometer etc. From which a positive or negative quantity is reckoned. 3 (attrib.) No, not any (zero growth). 4 (in full zero-hour) a hour at which a planned, esp. Military, operation is timed to begin. B crucial moment. 5 lowest or earliest point (down to zero; the year zero).  zero in on (-oes, -oed) 1 take aim at. 2 focus one's attention on. [arabic: related to *cipher]