adj.
first 有三个词性:名词 n.; 副词 adv.; 形容词 adj.
从例子可以感觉到不同:
1.名词:eg.I was the first in my family to go to college.
eg.She got a first in maths at Exeter.
2.副词:eg.Who came first in the race
eg.I'll finish my work first,then,have a drink.
3.形容词:eg.his first wife第一任妻子 ; the first time第一次 ; your first impressions第一印象 .