a most 和the most区别
a most 不是最高级的用法，此处的most表示“很，非常”的意思；
the most 是多音节形容词的最高级形式。
例句
Jim was a most loving husband and father.
A most unwelcome event claimed his attention.
一件最讨厌的事情需要他去考虑。
They are capable of the most heinous acts.
他们能做出令人发指的事情来。
The most popular spectator sport is football.
足球是最吸引观众的体育比赛。