Adverb (fukushi)
at full speed; (at) full tilt; headlong; impetuously; precipitately
Usually written using kana aloneusu. as 〜に
「ねこまっしぐら」というのは、飼い猫がエサに向かってまいしんする様子を表している。The phrase "make a bee line for" expresses the look of how a bee heads straight for food with speed and energy.
Also written 驀地【まっしぐら】