Many

The triliteral root kāf thā rā (ك ث ر) occurs in the Quran 167 times.

(2:26) God does not shy away from citing the example of a mosquito, or anything above it. As for those who acknowledge, they know that it is the truth from their Lord. As for the unappreciative, they say, "What did God intend by this example?" He lets many (Arab. كَثِيرًا, kathīran) stray by it, and He guides many (Arab. كَثِيرًا, kathīran), but He only lets stray the evildoers.

(74:6) And do not confer favor to acquire more (Arab. تَسْتَكْثِرُ, tastakthiru).